Amino acid transporters and uses

ABSTRACT

The present invention relates to novel mammalian amino acid transporter proteins and the genes that encode such proteins. The invention is directed toward the isolation, characterization and pharmacological use of a human amino acid transporter protein termed EAAT4 and genes encoding such a transporter. The invention specifically provides isolated complementary DNA copies of mRNA corresponding to this transporter gene. Also provided are recombinant expression constructs capable of expressing this amino acid transporter gene in cultures of transformed prokaryotic and eukaryotic cells, as well as such cultures of transformed cells that synthesize the human amino acid transporter protein encoded therein. The invention also provides methods for screening in vitro compounds having transport-modulating properties using preparations of transporter proteins from such cultures of cells transformed with recombinant expression constructs.

This invention was made with government support under National Institute of Health grant DA07595. The government has certain rights to this invention.

This application is a continuation-in-part of U.S. Ser. No. 08/140,729, filed Oct. 20, 1993, now U.S. Pat. No. 5,658,782, issued Aug. 19, 1997, which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to amino acid transporters from mammalian species and the genes corresponding to such transporters. Specifically, the invention relates to the isolation, cloning and sequencing of complementary DNA (cDNA) copies of messenger RNA (mRNA) encoding a novel human amino acid transporter gene. The invention also relates to the construction of recombinant expression constructs comprising such cDNAs from a novel human amino acid transporter gene of the invention, said recombinant expression constructs being capable of expressing amino acid transporter protein in cultures of transformed prokaryotic and eukaryotic cells as well as in amphibian oocytes. Production of the transporter protein of the invention in such cultures and oocytes is also provided. The invention relates to the use of such cultures of such transformed cells to produce homogeneous compositions of the novel transporter protein. The invention also provides cultures of such cells and oocytes expressing transporter protein for the characterization of novel and useful drugs. Antibodies against and epitopes of the transporter protein are also provided by the invention.

2. Background of the Invention

The approximately 20 naturally-occurring amino acids are the basic building blocks for protein biosynthesis. Certain amino acids, such as glutamate and glycine, as well as amino acid derivatives such as γ-aminobutyric acid (GABA), epinephrine and norepinephrine, and histamine, are also used as signaling molecules in higher organisms such as man. For these reasons, specialized trans-membrane transporter proteins have evolved in all organisms to recover or scavenge extracellular amino acids (see Christensen, 1990, Physiol. Rev. 70: 43-77 for review).

These transporter proteins play a particularly important role in uptake of extracellular amino acids in the vertebrate brain (see Nicholls & Attwell, 1990, TiPS 11: 462-468). Amino acids that function as neurotransmitters must be scavenged from the synaptic cleft between neurons to enable continuous repetitive synaptic transmission. More importantly, it has been found that high extracellular concentrations of certain amino acids (including glutamate and cysteine) can cause neuronal cell death. High extracellular amino acid concentrations are associated with a number of pathological conditions, including ischemia, anoxia and hypoglycemia, as well as chronic illnesses such as Huntington's disease, Parkinson's disease, Alzheimer's disease, epilepsy and amyotrophic lateral sclerosis (ALS; see Pines et al., 1992, Nature 360: 464-467).

Glutamate is one example of such an amino acid. Glutamate is an excitatory neurotransmitter (i.e., excitatory neurons use glutamate as a neurotransmitter). When present in excess (>about 300 μM; Bouvier et al., 1992, Nature 360: 471-474; Nicholls & Attwell, ibid.; >5 μM for 5 min.; Choi et al., 1987, J. Neurosci. 7: 357-358), extracellular glutamate causes neuronal cell death. Glutamate transporters play a pivotal role in maintaining non-toxic extracellular concentrations of glutamate in the brain. During anoxic conditions (such as occur during ischemia), the amount of extracellular glutamate in the brain rises dramatically. This is in part due to the fact that, under anoxic conditions, glutamate transporters work in reverse, thereby increasing rather than decreasing the amount of extracellular glutamate found in the brain. The resultingly high extracellular concentration of glutamate causes neuron death, with extremely deleterious consequences for motor and other brain functions, resulting in stroke and other instances of organic brain dysfunction.

This important role for amino acid transporters in maintaining brain homeostasis of extracellular amino acid concentrations has provided the impetus for the search for and development of compounds to modulate and control transporter function. However, conventional screening methods require the use of animal brain slices in binding assays as a first step. This is suboptimal for a number of reasons, including interference in the binding assay by non-specific binding of heterologous (i.e., non-transporter) cell surface proteins expressed by brain cells in such slices; differential binding by cells other than neuronal cells present in the brain slice, such as glial cells or blood cells; and the possibility that putative drug binding behavior in animal brain cells will differ from the binding behavior in human brain cells in subtle but critical ways. The ability to synthesize human transporter molecules in vitro would provide an efficient and economical means for rational drug design and rapid screening of potentially useful compounds.

Amino acid transporters are known in the art, and some of these proteins have been isolated biochemically and their corresponding genes have been recently cloned using genetic engineering means.

Christensen et al., 1967, J. Biol. Chem. 242: 5237-5246 report the discovery of a neutral amino acid transporter (termed the ACS transporter) in Erlich ascites tumor cells.

Makowske & Christensen, 1982, J. Biol. Chem. 257: 14635-14638 provide a biochemical characterization of hepatic amino acid transport.

Kanner & Schuldiner, 1987, CRC Crit. Rev. Biochem. 22: 1-38 provide a review of the biochemistry of neurotransmitters.

Olney et al., 1990, Science 248: 596-599 disclose that the amino acid cysteine is a neurotoxin when present in excess extracellularly.

Wallace et al., 1990, J. Bacteriol. 172: 3214-3220 report the cloning and sequencing of a glutamate/aspartate transporter gene termed gltP from Escherichia coli strain K12.

Kim et al., 1991, Nature 352: 725-728 report the discovery that a cationic amino acid transporter is the cell surface target for infection by ecotropic retroviruses in mice.

Wang et al., 1991, Nature 352: 729-731 report the discovery that a cationic amino acid transporter is the cell surface target for infection by ecotropic retroviruses in mice.

Maenz et al., 1992, J. Biol. Chem. 267: 1510-1516 provide a biochemical characterization of amino acid transport in rabbit jejunal brush border membranes.

Bussolati et al., 1992, J. Biol. Chem. 267: 8330-8335 report that the ASC transporter acts in an electrochemically neutral manner so that sodium ion co-transport occurs without disrupting the normal membrane potential of the cells expressing the transporter.

Engelke et al., 1992, J. Bacteriol. 171: 5551-5560 report the cloning of a dicarboxylate carrier from Rhizobium meliloti.

Guastella et al., 1992, Proc. Natl. Acad. Sci. USA 89: 7189-7193 disclose the cloning of a sodium ion and chloride ion-dependent glycine transporter from a glioma cell line that is expressed in the rat forebrain and cerebellum.

Kavanaugh et al., 1992, J. Biol. Chem. 267: 22007-22009 report biochemical characterization of a rat brain GABA transporter expressed in vitro in Xenopus laevis oocytes.

Storck et al., 1992, Proc. Natl. Acad. Sci. USA 89: 10955-10959 disclose the cloning and sequencing of a sodium ion-dependent glutamate/ aspartate transporter from rat brain termed GLAST1.

Bouvier et al., ibid., disclose the biochemical characterization of a glial cell-derived glutamate transporter.

Pines et al., ibid., report the cloning and sequencing of a glial cell glutamate transporter from rat brain termed GLT-1.

Kanai & Hediger, 1992, Nature 360: 467-471 disclose the cloning and sequencing of a sodium ion-dependent, high affinity glutamate transporter from rabbit small intestine termed EAAC1.

Arriza et al., 1992, J. Biol. Chem. 268: 15329-15332 disclose a gene for a novel neutral amino acid transporter.

Kong et al., 1993, J. Biol. Chem. 268: 1509-1512 report the cloning and sequencing of a sodium-ion dependent neutral amino acid transporter of the A type that is homologous to a sodium-ion dependent glucose transporter.

Arriza et al., 1994, J. Neurosci. 14: 5559-5569 disclose genes for three novel glutamate transporters.

Nicholls & Attwell, ibid., review the role of amino acids and amino acid transporters in normal and pathological brain functions.

SUMMARY OF THE INVENTION

The present invention relates to the cloning, expression and functional characterization of mammalian amino acid transporter genes. The invention comprises nucleic acids having a nucleotide sequence of a novel amino acid transporter gene. The nucleic acids provided by the invention each comprise a complementary DNA (cDNA) copy of the corresponding mRNA transcribed in vivo from the amino acid transporter gene of the invention. Also provided is the deduced amino acid sequences of the cognate protein of the cDNA provided by the invention.

This invention provides nucleic acids, nucleic acid hybridization probes, recombinant eukaryotic expression constructs capable of expressing the amino acid transporter of the invention in cultures of transformed cells and in amphibian oocytes, such cultures of transformed eukaryotic cells and such amphibian oocytes that synthesize the amino acid transporter of the invention, a homogeneous composition of the amino acid transporter protein, and antibodies against and epitopes of the amino acid transporter protein of the invention. Methods for characterizing this transporter protein and methods for using this protein and cells and oocytes expressing this protein for the development of agents having pharmacological uses related to this transporter protein are also provided by the invention.

In a first aspect, the invention provides a nucleic acid having a nucleotide sequence encoding a human excitatory amino acid transporter that is the EAAT4 transporter (SEQ ID No:1). In this embodiment of the invention, the nucleotide sequence includes 1734 nucleotides of the human EAAT4 cDNA comprising 1692 nucleotides of coding sequence, 8 nucleotides of 5' untranslated sequence and 34 nucleotides of 3' untranslated sequence. In this embodiment of the invention, the nucleotide sequence of the EAAT4 transporter is the nucleotide sequence depicted in FIGS. 1A through 1C (SEQ ID No:1).

In another aspect, the invention comprises a homogeneous composition of the 61.6 kilodalton (kD) mammalian EAAT4 transporter and derivatives thereof, said size being understood to be the size of the protein before any post-translational modifications thereof. The amino acid sequence of the EAAT4 transporter and derivatives thereof preferably is the amino acid sequence of the human EAAT4 transporter protein shown in FIGS. 2A through 2C (SEQ ID No:2). EAAT4 protein molecules provided by the invention are understood to have substantially the same biological properties as the EAAT4 protein molecule encoded by the nucleotide sequence described herein.

This invention provides both nucleotide and amino acid probes derived from the sequences herein provided. The invention includes probes isolated from either cDNA or genomic DNA, as well as probes made synthetically with the sequence information derived therefrom. The invention specifically includes but is not limited to oligonucleotide, nick-translated, random primed, or in vitro amplified probes made using cDNA or genomic clone embodiments of the invention, and oligonucleotide and other synthetic probes synthesized chemically using the nucleotide sequence information of cDNA or genomic clone embodiments of the invention.

It is a further object of this invention to provide such nucleic acid hybridization probes to determine the pattern, amount and extent of expression of this transporter gene in various tissues of mammals, including humans. It is also an object of the present invention to provide nucleic acid hybridization probes derived from the sequences of the amino acid transporter gene of the invention to be used for the detection and diagnosis of genetic diseases. It is an object of this invention to provide nucleic acid hybridization probes derived from the DNA sequence of the amino acid transporter gene herein disclosed to be used for the detection of novel related receptor genes.

The present invention also includes synthetic peptides made using the nucleotide sequence information comprising the cDNA embodiments of the invention. The invention includes either naturally occurring or synthetic peptides which may be used as antigens for the production of amino acid transporter-specific antibodies, or used for competitors of amino acid transporter molecules for amino acid, agonist, antagonist or drug binding, or to be used for the production of inhibitors of the binding of agonists or antagonists or analogues thereof to such amino acid transporter molecules.

The present invention also provides antibodies against and epitopes of the mammalian amino acid transporter molecules of the invention. It is an object of the present invention to provide antibodies that are immunologically reactive to the amino acid transporter of the invention. It is a particular object to provide monoclonal antibodies against this amino acid transporter, most preferably the human excitatory amino acid transporter as herein disclosed. Hybridoma cell lines producing such antibodies are also objects of the invention. It is envisioned that such hybridoma cell lines may be produced as the result of fusion between a non-immunoglobulin producing mouse myeloma cell line and spleen cells derived from a mouse immunized with a cell line which expresses antigens or epitopes of an amino acid transporter of the invention. The present invention also provides hybridoma cell lines that produce such antibodies, and can be injected into a living mouse to provide an ascites fluid from the mouse that is comprised of such antibodies. It is a further object of the invention to provide immunologically-active epitopes of the amino acid transporter of the invention. Chimeric antibodies inununologically reactive against the amino acid transporter protein of the invention are also within the scope of this invention.

The present invention provides recombinant expression constructs comprising a nucleic acid encoding an amino acid transporter of the invention wherein the construct is capable of expressing the encoded amino acid transporter in cultures of cells or amphibian oocytes transformed with the construct. Preferred embodiments of such constructs comprise the human EAAT4 cDNA (SEQ ID No.:1), the construct being capable of expressing the amino acid transporter encoded therein in cells and oocytes transformed with the construct or into which the construct has otherwise been introduced.

The invention also provides cultured cells transformed with the recombinant expression constructs of the invention, each such culture being capable of and in fact expressing the amino acid transporter encoded in the transforming construct. The invention also provides amphibian oocytes into which a recombinant expression construct of the invention is introduced, each such oocyte being capable of and in fact expressing the amino acid transporter encoded in the transforming construct.

The present invention also includes within its scope protein preparations of prokaryotic and eukaryotic cell membranes containing the amino acid transporter protein of the invention, derived from cultures of prokaryotic or eukaryotic cells, respectively, transformed with the recombinant expression constructs of the invention. In a preferred embodiment, such preparations of cell membranes comprise the amino acid transporter protein of the invention.

The invention also provides methods for screening compounds for their ability to inhibit, facilitate or modulate the biochemical activity of the amino acid transporter molecules of the invention, for use in the in vitro screening of novel agonist and antagonist compounds. In preferred embodiments, cells, particularly amphibian oocytes transformed with a recombinant expression construct of the invention are contacted with such a compound, and the effect of the compound on the transport of the appropriate amino acid is assayed. Additional preferred embodiments comprise quantitative analyses of such effects. Also provided are assays that distinguish between the effect of such compounds on amino acid transport from effects of such compounds on chloride ion transport by the transporters of the invention.

The present invention is also useful for the detection of analogues, agonists or antagonists, heretofore known or unknown, of the amino acid transporters of the invention, either naturally occurring or embodied as a drug. In preferred embodiments, such analogues, agonists or antagonists may be detected in blood, saliva, semen, cerebrospinal fluid, plasma, lymph, or any other bodily fluid. In additional preferred embodiments, the invention provides methods for detecting and identifying analogues, agonists or antagonists that preferentially affect either the amino acid uptake function or the chloride ion channel function of the amino acid transporters of the invention.

Specific preferred embodiments of the present invention will become evident from the following more detailed description of certain preferred embodiments and the claims.

DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1C illustrates the nucleotide (SEQ ID No.:1) sequence of the human EAAT4 excitatory amino acid transporter.

FIGS. 2A through 2C illustrates the amino acid (SEQ ID No.:2) sequence of the human EAAT4 excitatory amino acid transporter.

FIG. 3 presents an amino acid sequence comparison between human EAAT4 and the previously-disclosed excitatory amino acid transporters EAAT1 (SEQ ID Nos.: 3& 4), EAAT2 (SEQ ID Nos.: 5&6) and EAAT3 (SEQ ID Nos.: 7&8).

FIG. 4 shows the pattern of expression of EAAT4 mRNA in human brain tissue; β-actin is shown as a control for the amount of RNA in each lane.

FIG. 5 shows the pattern of expression of EAAT4 mRNA in human tissues; β-actin is shown as a control for amount of RNA in each lane.

FIG. 6A illustrates transmembrane electrochemical currents in Xenopus laevis oocytes microinjected with RNA encoding EAAT4 cRNA and contacted with 10 μM L-aspartate at varying voltage-clamped voltages. The magnitude of the induced current and the time course of induction are shown with reference to the indicator bars in the upper right-hand corner of the Figure.

FIG. 6B is a graph showing the relationship between the magnitude of the applied voltage clamp and the induced current in the presence of increasing amounts of gluconate ion in substitution for chloride ion. Open circles correspond to 104 mM chloride ion (no gluconate ion present), closed circles correspond to 56 mM chloride ion, open squares correspond to 20 mM chloride ion and closed squares correspond to 0 mM chloride ion (i.e., chloride ion is substituted entirely by gluconate ion).

FIG. 6C is a semilogarithmic plot of the reversal potential versus the log of the chloride ion concentration, showing that the application of excitatory amino acids to EAAT4 induces a large chloride ion current.

FIG. 6D illustrates transmembrane electrochemical currents in Xenopus oocytes microinjected with RNA encoding EAAT4 cRNA and contacted with 10 μM L-aspartate in the presence and absence of sodium ion in the perfusate. The magnitude of the induced current and the time course of induction are shown with reference to the indicator bars in the upper right-hand corner of the Figure.

FIG. 7A is a graph illustrating the current-voltage (I-V) relationship typical for EAAT1, EAAT2, and EAAT3, illustrated for EAAT-2. In this example, the application of L-glutamate to EAAT2, there is inward rectification of the current, and outward currents are seen only at membrane potentials more positive than +40 mV.

FIG. 7B is a graph showing the concentration and voltage dependence of L-aspartate induced currents in EAAT4 . The current is dose-dependent, linear, and reverses (becomes outward) at a membrane potential of ˜-20 mV. L-aspartate concentrations shown are 0.3 μm (filled circles), 1 μM (open circles), 10 μM (open diamonds), and 100 μM (filled diamonds).

FIG. 7C is a graph comparing the current-voltage relationships of L-aspartate and L-glutamate, for concentrations of 100 μM L-aspartate (filled circles) and 100 μM L-glutamate (open circles).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term "human amino acid transporter EAAT4" as used herein refers to proteins having substantially the same biological activity as the protein encoded by the nucleic acid depicted in FIGS. 2A through 2C (SEQ ID No.: 1). This definition is intended to encompass allelic variations in the EAAT4 sequence, either naturally occurring or the product of in vitro chemical or genetic modification. Each such variant will be understood to have essentially the same nucleotide sequence as the nucleotide sequence of the corresponding EAAT4 disclosed herein. Cloned nucleic acid provided by the present invention may encode EAAT4 protein of any species of origin, including, for example, mouse, rat, rabbit, cat, and human, but preferably the nucleic acid provided by the invention encodes EAAT4 receptors of mammalian, most preferably human, origin.

The term "excitatory amino acid" is intended to encompass naturally-occurring and synthetic amino acids such as L-aspartate and L-glutamate, as well as homologues, analogues or derivatives thereof. The terms is also intended to encompass agonists, antagonists and inhibitors of mammalian glutamate receptors.

The term "detectably labeled" is intended to encompass any reporter molecule capable of being detected by radiometric, fluorescent, spectrophotometric or other physical or chemical means. Particular examples include radiolabels, including but not limited to ³ H and ¹⁴ C.

The term "chloride equilibrium potential" is intended to mean the membrane potentiat at which there is no detectable chloride ion flux across the cell membrane.

The nucleic acid hybridization probes provided by the invention comprise DNA or RNA having the nucleotide sequence of the amino acid transporters, depicted in FIGS. 1A through 1C (SEQ ID No.:1), or any portion thereof effective in nucleic acid hybridization under stringency conditions sufficient to permit specific hybridization of the probe to a complementary nucleic acid sequence. Mixtures of such nucleic acid hybridization probes are also within the scope of this embodiment of the invention. Nucleic acid probes as provided herein are useful for detecting novel amino acid transporter genes related to the EAAT4 gene disclosed herein, specifically including homologous or syntenic transporter genes in non-human mammalian species. Nucleic acid probes as provided herein are also useful for detecting amino acid transporter gene expression in cells and tissues using techniques well-known in the art, including but not limited to Northern blot hybridization, in situ hybridization and Southern hybridization to reverse transcriptase-polymerase chain reaction (RT-PCR) product DNAs. The probes provided by the present invention, including oligonucleotide probe derived therefrom, are also useful for Southern hybridization of mammalian, preferably human, genomic DNA for screening for restriction fragment length polymorphism (RFLP) associated with genetic disorders.

The production of proteins such as these amino acid transporter molecules from cloned genes by genetic engineering means is well known in this art. The discussion which follows is accordingly intended as an overview of this field, and is not intended to reflect the full state of the art.

DNA encoding an amino acid transporter may be obtained, in view of the instant disclosure, by chemical synthesis, by screening reverse transcripts of mRNA from appropriate cells or cell line cultures, by screening genomic libraries from appropriate cells, or by combinations of these procedures, as illustrated below. Screening of mRNA or genomic DNA may be carried out with oligonucleotide probes generated from the nucleic acid sequence information from each of the amino acid transporters disclosed herein. Probes may be labeled with a detectable group such as a fluorescent group, a radioactive atom or a chemiluminescent group in accordance with know procedures and used in conventional hybridization assays, as described in greater detail in the Examples below. In the alternative, amino acid transporter-derived nucleic acid sequences may be obtained by use of the polymerase chain reaction (PCR) procedure, using PCR oligonucleotide primers corresponding to nucleic acid sequence information derived from an amino acid transporter as provided herein. See U.S. Pat. No. 4,683,195 to Mullis et al. and U.S. Pat. No. 4,683,202 to Mullis.

The amino acid transporter protein of the invention may be synthesized in host cells, in particular amphibian oocytes, transformed with a recombinant expression construct comprising a nucleic acid encoding amino acid transporter cDNA. Such recombinant expression constructs can also be comprised of a vector that is a replicable DNA construct. Vectors are used herein either to amplify DNA encoding an amino acid transporter and/or to express DNA encoding an amino acid transporter gene. For the purposes of this invention, a recombinant expression construct is a replicable DNA construct in which a nucleic acid encoding an amino acid transporter is operably linked to suitable control sequences capable of effecting the expression of the amino acid transporter in a suitable host or host cell.

The need for such control sequences will vary depending upon the host selected and the transformation method chosen. Generally, control sequences include a transcriptional promoter, optional or ancillary transcription control sequences, such as transcription factor binding domains, enhancer sequences, and other eukaryotic "operator" sequences to control transcription, a sequence encoding suitable mRNA ribosomal binding sites, and sequences which control the termination of transcription and translation. Amplification vectors do not require expression control domains. All that is needed is the ability to replicate in a host, usually conferred by an origin of replication, and a selection gene to facilitate recognition of transformants. See, Sambrook et al., 1990, Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Press: New York).

Vectors useful for practicing the present invention include plasmids, viruses (including phage), retroviruses, and integratible DNA fragments (i.e., fragments integratible into the host genome by homologous recombination). The vector replicates and functions independently of the host genome, or may, in some instances, integrate into the genome itself. Suitable vectors will contain replicon and control sequences which are derived from species compatible with the intended expression host. A preferred vector is pCMV5 (Andersson et al., 1989, J. Biol. Chem. 264: 8222-8229). Transformed host cells are cells which have been transformed or transfected with recombinant expression constructs made using recombinant DNA techniques and comprising nucleic acid encoding an amino acid transporter protein. Preferred host cells are Xenopus laevis oocytes, oocytes from other amphibian species, and COS-7 cells (Gluzman, 1981, Cell 23: 175-182). Transformed host cells may express the amino acid transporter protein, but host cells transformed for purposes of cloning or amplifying nucleic acid hybridization probe DNA need not express the transporter. When expressed, the amino acid transporter protein molecules of the invention will typically be located in the host cell membrane. See, Sambrook et al., ibid.

Cultures of cells derived from multicellular organisms are a desirable host for recombinant amino acid transporter protein synthesis. In principal, any higher eukaryotic cell culture is useful, whether from vertebrate or invertebrate culture. However, mammalian cells are preferred, as illustrated in the Examples. Propagation of such cells in cell culture has become a routine procedure. See Tissue Culture, Academic Press, Kruse & Patterson, editors (1973). Examples of useful host cell lines are human 293 cells, VERO and HeLa cells, Chinese hamster ovary (CHO) cell lines, and WI138, BHK, COS-7, CV, and MDCK cell lines. COS-7 cells are preferred.

Certain other primary host cells, not subjected to prolonged tissue culture adaptation, can be used to produce the amino acid transporters of the invention, particularly amphibian oocytes. Amphibian oocytes are useful for expressing the mammalian excitatory transporters of this invention, most preferably oocytes from Xenopus laevis or other amphibian, which oocytes are used to provide cells convenient for the practice of some of the inventive methods disclosed herein.

Thus, the invention also provides a method for making the human EAAT4 amino acid transporters of the invention, and membrane preparations comprising this transporter, by introducing nucleic acid encoding the transporter into an appropriate prokaryotic, or preferably, eukaryotic, most preferably mammalian, cell that is capable of expressing the transporter protein.

The invention provides homogeneous compositions of the human EAAT4 amino acid transporter proteins produced by transformed eukaryotic cells as provided herein. Such a homogeneous compositions is intended to be comprised of the corresponding amino acid transporter protein that comprises at least 50-90% of the protein in such a homogenous composition. The invention also provides membrane preparations from cells expressing the amino acid transporter protein as the result of transformation with a recombinant expression construct, as described herein.

Amino acid transporter protein made from cloned genes in accordance with the present invention may be used for screening amino acid analogues, or inhibitors, agonists or antagonists of amino acid transport, or for determining the amount of such agonists or antagonists in a solution of interest (e.g., blood plasma or serum). For example, host cells may be transformed with a recombinant expression construct of the present invention, an amino acid transporter expressed in those host cells, and the cells or membranes thereof used to screen compounds for their effect on amino acid transport activity. By selection of host cells that do not ordinarily express a particular amino acid transporter, pure preparations of membranes containing the transporter can be obtained.

The recombinant expression constructs of the present invention are useful in molecular biology to transform cells which do not ordinarily express a particular amino acid transporter to thereafter express this receptor. Such cells are useful as intermediates for making cell membrane preparations useful for transporter activity assays, which are in turn useful for drug screening. The recombinant expression constructs of the present invention may also be useful in gene therapy. Cloned genes of the present invention, or fragments thereof, may also be used in gene therapy carried out using homologous recombination or site-directed mutagenesis. See generally Thomas & Capecchi, 1987, Cell 51: 503-512; Bertling, 1987, Bioscience Reports 7: 107-112; Smithies et al., 1985, Nature 317: 230-234.

Oligonucleotides of the present invention are useful as diagnostic tools for probing amino acid transporter gene expression in tissues of humans and other animals. For example, tissues are probed in situ with oligonucleotide probes carrying detectable groups by conventional autoradiographic techniques, to investigate native expression of this receptor or pathological conditions relating thereto. Further, chromosomes can be probed to investigate the presence or absence of the corresponding amino acid transporter gene, and potential pathological conditions related thereto.

The invention also provides antibodies that are immunologically reactive to the amino acid transporter protein or epitopes thereof provided by the invention. The antibodies provided by the invention may be raised, using methods well known in the art, in animals by inoculation with cells that express an amino acid transporter or epitopes thereof, cell membranes from such cells, whether crude membrane preparations or membranes purified using methods well known in the art, or purified preparations of proteins, including fusion proteins, particularly fusion proteins comprising epitopes of the amino acid transporter protein of the invention fused to heterologous proteins and expressed using genetic engineering means in bacterial, yeast or eukaryotic cells, said proteins being isolated from such cells to varying degrees of homogeneity using conventional biochemical means. Synthetic peptides made using established synthetic means in vitro and optionally conjugated with heterologous sequences of amino acids, are also encompassed in these methods to produce the antibodies of the invention. Animals that are used for such inoculations include individuals from species comprising cows, sheep, pigs, mice, rats, rabbits, hamsters, goats and primates. Preferred animals for inoculation are rodents (including mice, rats, hamsters) and rabbits. The most preferred animal is the mouse.

Cells that can be used for such inoculations, or for any of the other means used in the invention, include any cell line which naturally expresses the amino acid transporter provided by the invention, or any cell or cell line that expresses the amino acid transporter of the invention, or any epitope thereof, as a result of molecular or genetic engineering, or that has been treated to increase the expression of an endogenous or heterologous amino acid transporter protein by physical, biochemical or genetic means. Preferred cells are E. coli and insect SF9 cells, most preferably E. coli cells, that have been transformed with a recombinant expression construct of the invention encoding an amino acid transporter protein, and that express the transporter therefrom.

The present invention also provides monoclonal antibodies that are immunologically reactive with an epitope derived from an amino acid transporter of the invention, or fragment thereof, present on the surface of such cells, preferably E. coli cells. Such antibodies are made using methods and techniques well known to those of skill in the art. Monoclonal antibodies provided by the present invention are produced by hybridoma cell lines, that are also provided by the invention and that are made by methods well known in the art.

Hybridoma cell lines are made by fusing individual cells of a myeloma cell line with spleen cells derived from animals immunized with cells expressing an amino acid transporter of the invention, as described above. The myeloma cell lines used in the invention include lines derived from myelomas of mice, rats, hamsters, primates and humans. Preferred myeloma cell lines are from mouse, and the most preferred mouse myeloma cell line is P3X63-Ag8.653. The animals from whom spleens are obtained after immunization are rats, mice and hamsters, preferably mice, most preferably Balb/c mice. Spleen cells and myeloma cells are fused using a number of methods well known in the art, including but not limited to incubation with inactivated Sendai virus and incubation in the presence of polyethylene glycol (PEG). The most preferred method for cell fusion is incubation in the presence of a solution of 45% (w/v) PEG-1450. Monoclonal antibodies produced by hybridoma cell lines can be harvested from cell culture supernatant fluids from in vitro cell growth; alternatively, hybridoma cells can be injected subcutaneously and/or into the peritoneal cavity of an animal, most preferably a mouse, and the monoclonal antibodies obtained from blood and/or ascites fluid.

Monoclonal antibodies provided by the present invention are also produced by recombinant genetic methods well known to those of skill in the art, and the present invention encompasses antibodies made by such methods that are immunologically reactive with an epitope of an amino acid transporter of the invention. The present invention also encompasses fragments, including but not limited to F(ab) and F(ab)₂ fragments, of such antibody. Fragments are produced by any number of methods, including but not limited to proteolytic cleavage, chemical synthesis or preparation of such fragments by means of genetic engineering technology. The present invention also encompasses single-chain antibodies that are immunologically reactive with an epitope of an amino acid transporter, made by methods known to those of skill in the art.

The present invention also encompasses an epitope of an amino acid transporter of the invention, comprised of sequences and/or a conformation of sequences present in the transporter molecule. This epitope may be naturally occurring, or may be the result of proteolytic cleavage of a transporter molecule and isolation of an epitope-containing peptide or may be obtained by synthesis of an epitope-containing peptide using methods well known to those skilled in the art. The present invention also encompasses epitope peptides produced as a result of genetic engineering technology and synthesized by genetically engineered prokaryotic or eukaryotic cells.

The invention also includes chimeric antibodies, comprised of light chain and heavy chair peptides immunologically reactive to an amino acid transporter-derived epitope. The chimeric antibodies embodied in the present invention include those that are derived from naturally occurring antibodies as well as chimeric antibodies made by means of genetic engineering technology well known to those of skill in the art.

The invention also provides methods for screening compounds for their ability to inhibit, facilitate or modulate the biochemical activity of the amino acid transporter molecules of the invention, for use in the in vitro screening of novel agonist and antagonist compounds. In preferred embodiments, cells, particularly amphibian oocytes transformed with a recombinant expression construct of the invention are contacted with such a compound, and the effect of the compound on the transport of the appropriate amino acid is assayed. Additional preferred embodiments comprise quantitative analyses of such effects. Also provided are assays that distinguish between the effect of such compounds on amino acid transport from effects of such compounds on chloride ion transport by the transporters of the invention.

The present invention is also useful for the detection of inhibitors, analogues, agonists or antagonists, heretofore known or unknown, of the amino acid transporters of the invention, either naturally occurring or embodied as a drug. In preferred embodiments, such inhibitors, analogues, agonists or antagonists may be detected in blood, saliva, semen, cerebrospinal fluid, plasma, lymph, or any other bodily fluid. In additional preferred embodiments, the invention provides methods for detecting and identifying inhibitors, analogues, agonists or antagonists that preferentially affect either the amino acid uptake function or the chloride ion channel function of the amino acid transporters of the invention.

The Examples which follow are illustrative of specific embodiments of the invention, and various uses thereof. They set forth for explanatory purposes only, and are not to be taken as limiting the invention.

EXAMPLE 1 Isolation of a Human Excitatory Amino Acid Transporter cDNA

Excitatory amino acid transporters EAAT1, EAAT2 and EAAT3 have been disclosed in co-owned and co-pending U.S. Ser. No. 08/140,729, filed Oct. 20, 1993, now U.S. Pat. No. 5,658,782, issued Aug. 19, 1997, which is incorporated by reference herein in its entirety.

In order to clone a novel human excitatory amino acid transporter, cDNA was prepared from human cerebellar mRNA and amplified in vitro using a pair of degenerate primers derived from two regions of sequence similarity between the EAAT1, EAAT2 and EAAT3 genes previously disclosed. Briefly, total RNA was isolated using the method of Chomczynski & Sacchi (1987, Anal. Biochem. 162: 156-159), wherein the tissue is disrupted and solubilized in a solution containing guanidinium isothiocyanate and the RNA purified by phenol/chloroform extractions. Total cellular RNA thus isolated was then enriched for poly (A⁺) mRNA by oligo (dT) chromatography. A mixture of oligo (dT)-primed and random-primed mRNA was converted to cDNA using the Superscript Choice System (Bethesda Research Labs, Gaithersburg, Md.). 10 ng of this cerebellum-derived cDNA preparation was then amplified using the following degenerate oligonucleotide primers:

Sense primer

5'-CGCGGGTACCAA(T/C)CT(C/G)GT(C/A/G)(G/C)A(G/A)GC(T/C)TG(T/C)TT(T/C)-3' (SEQ ID NO:9);

Antisense primer

5'-CGCGTCTAGA(T/C)TG(A/G/T)GC(A/G/T)AT(A/G)AA(A/G)A(T/C)(G/T/C)GC(A/G/T)GC-3' (SEQ ID NO:10).

PCR amplification was performed for 35 cycles, each cycle comprising 1 minute at 94° C., 1 min at 47° C. and 2 minutes at 72° C. using Vent polymerase (New England Biolabs, Beverly, Mass.). Following the PCR, the product of the amplification reaction was purified using standard techniques (Saiki et al., 1988, Science 239: 487-491).

Novel candidate clones were identified by the following hybridization strategy. Bona fide transporter cDNAs were identified by hybridization with the following degenerate oligonucleotide probe for a highly conserved coding sequence:

5'-CTGRGCRATGAARATGGCAGCCAGGGCYTCATACAGGGCTGTGCCRTCCATGTTRATGGTRGC-3' (SEQ ID No.:11) (See Arriza et al., 1992, ibid.). Those transporter cDNAs previously isolated (i.e., encoding EAAT1, EAAT2 , EAAT3 , ASCT1) were identified by specific hybridization with their previously-isolated cDNA probes under high stringency conditions (e.g., 0.1× SSC (standard citrate saline)/1% SDS (sodium dodecyl sulfate) at 65° C. (see Sambrook et al., 1990, Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Press: New York))). cDNAs that hybridized with the oligonucleotide but did not correspond to previously isolated cDNAs were characterized by nucleotide sequence analysis.

A novel clone similar to the previously-identified glutamate transporters was identified. This novel PCR amplification product was used to screen a motor cortex mRNA prepared using standard techniques (see Sambrook et al., ibid.). Total RNA was isolated using the method of Chomczynski & Sacchi as above, and then enriched for poly (A⁺) mRNA by oligo (dT) chromatography. A mixture of oligo (dT)-primed and random-primed mRNA was converted to cDNA using the Superscript Choice System and the cDNA was then ligated into the cloning vector λZAPII (Strategene, La Jolla, Calif.), packaged into phage heads using commercially-available packaging extracts (Strategene) and used to infect E. coli. Lawns of infected bacterial cells were used to make plaque lifts for hybridization using standard conditions (see Sambrook, et al., ibid.).

This cDNA library was hybridized with the ³² P-labeled PCR amplification product described above. Hybridization was performed at 50° C. in a solution containing 0.5M Na₂ HPO₄ (pH 7.15)/ 7% sodium dodecyl sulfate (SDS) and the filters were washed at 60° C. in 2× SSPE (0.36M NaCl/ 20 mM sodium phosphate (pH 7.7)/ 2 mM ethylenediamine tetraacetic acid (EDTA)) and 1% SDS. Hybridizing clones were identified by autoradiography at -70° C. using tungsten-containing intensifying screens (DuPont-NEN, Wilmington, Del.).

Two independent clones containing 2.2 and 2.3 kilobase pair (kb) cDNA inserts were isolated. cDNA inserts were excised from the cloning vector in vivo by superinfection with a defective filamentous phage that recognizes and excises cloned insert sequences along with adjacent modified phage replication-form sequences (termed pBluescript SK and available from Strategene). Each clone was then sequenced using the dideoxy-chain termination method of Sanger et al. (1977, Proc. Natl. Acad. Sci. USA 74: 5463), using Sequenase 2.0, a modified form of bacteriophage T7 DNA polymerase (U.S. Biochemical Corp., Cleveland, Ohio). The two independent clones contained identical long open reading frames, and were identical in those regions of the 3' untranslated sequences analyzed. Each clone had a distinct 5' untranslated sequence but were identical in the 8 nucleotides upstream of the putative translation start site. This observation may be indicative of alternative RNA splicing in the 5' untranslated region of the EAAT4 gene. The 1734 nucleotide sequence of the human EAAT4 cDNA shown in FIGS. 1A through 1C includes the conserved 8 nucleotides of the 5' untranslated region, 34 nucleotides of the 3' untranslated region downstream of the translation stop codon, and 1692 nucleotides of coding sequence comprising 564 amino acids (FIGS. 2A through 2C and FIG. 3).

The EAAT4 amino acid sequence (SEQ ID No.:2; shown in FIGS. 2A through 2C) was found to exhibit similarity to other known glutamate transporter subtypes (an amino acid sequence comparison is shown in FIG. 3). An amino acid comparison between these 4 human glutamate transporters showed 65%, 41% and 48% sequence identity (respectively) between EAAT4 and EAAT1, EAAT2 and EAAT3 (shown in FIG. 3 by shaded boxes). Both the amino and carboxyl termini were found to be divergent between these transporter proteins, and diversity was also found in the extracellular domains of these putative protein sequences, which contain conserved potential N-glycosylation sites (shown in FIG. 3 by open boxes). It was noted that previously-identified sequence (comprising the amino acids --AA(I/V)FIAQ--) that was highly conserved in the glutamate transporters was also present in EAAT4 (at positions 434-440 of the EAAT4 amino acid sequence shown in FIGS. 2A through 2C). 6-10 putative transmembrane domains were found using the algorithm of Eisenberg et al. (1984, J. Molec. Biol. 179: 125-142). On the basis of these data EAAT4 was determined to encode a related but distinct and novel member of the excitatory amino acid transporter family.

EXAMPLE 2 Tissue Distribution of Amino Acid Transporter Expression

The tissue distribution of mRNA corresponding to expression of the EAAT4 amino acid transporter disclosed herein was determined in various tissues by Northern hybridization experiments (see Sambrook et al., ibid.). The results of these experiments are shown in FIGS. 4 and 5.

A panel of tissue samples was examined by Northern hybridization analysis performed under high stringency conditions as follows. A nylon filter containing 2 μg human peripheral tissue poly(A)⁺ RNA was obtained from Clonetech Laboratories (Palo Alto, Calif.), and a similar filter was prepared containing human brain region RNA as follows. Total RNA was isolated from human brain region tissue obtained from the Oregon Brain Repository and 20 μg/ region were size-fractionated by denaturing formaldehyde agarose gel electrophoresis (see Sambrook et al., ibid.). Fractionated RNA was then transferred to a nylon filter using the Northern blot/ capillary-osmotic technique. Northern hybridization of both filters was performed individually with a ³² P-labeled 1.7 kb EAAT4-specific probe prepared by random-primed synthesis (Boehringer Mannheim, Indianapolis, Ind.) using α-³² P-labeled dCTP. Filters were hybridized overnight at 42° C. individually with each radiolabeled probe (at a concentration of 10⁶ cpm/mL) in a solution of 5× SSPE/ 50% formamide/ 7.5× Denhardt's solution (comprising 0.15 g/100 mL each of Ficoll, polyvinylpyrrolidone and bovine serum albumin)/ 2% SDS and 100 μg/mL denatured salmon-sperm DNA. Following hybridization, filters were washed twice for 30 min at room temperature in 2× SSPE/ 0.1% SDS and twice for 20 min at 50° C. in 0.1× SSPE/ 0.1% SDS. Hybridizing RNAs were visualized by autoradiography at -70° C. using intensifying screens. The filters were subsequently re-probed as described with a radiolabeled human β-actin probe (Clonetech) as a positive control.

The results of these experiments, shown in FIGS. 4 and 5, demonstrate that EAAT4 transporter has a distribution distinct from other transporters isolated to date. FIG. 4 shows the distribution of these amino acid transporter transcripts in different human brain regions. Expression of the 2.4 kb EAAT4 mRNA was detected only in cerebellum using this Northern blot assay. However, a more sensitive polymerase chain reaction-based assay revealed EAAT4 expression in brain stem, cortex and hippocampus, albeit at much lower levels than those seen in cerebellum.

FIG. 5 illustrates expression of the EAAT4 transporter in human heart, brain, placenta, lung, liver, muscle, kidney and pancreas. The size (in kb) of the transcripts corresponding to expression of this transporter are displayed along the right-hand border of each panel. As is seen from these autoradiographs, EAAT4 was found to be expressed predominantly in brain and placenta as a single, 2.4 kb transcript, consistent with the size of the isolated cDNA clones.

These results support the conclusion that the amino acid transporter of the invention may play an important role in normal brain function, and that disruption of amino acid transport by this transporter may be important determinants in organic brain dysfunction, as a result of ischemia or anoxia. Moreover, because of the presumed role of the cerebellum in motor learning, the abundant expression of EAAT4 mRNA in the cerebellum suggests that this protein may be significant in both normal and dysfunctional (e.g., ataxia and related syndromes) motor coordination.

EXAMPLE 3 Functional Expression of the EAAT4 Amino Acid Transporter Gene in Xenopus Oocytes

The sequence similarity between EAAT4 and the previously-identified glutamate transporters EAAT1, EAAT2 and EAAT3 suggested that the protein encoded by the EAAT4 cDNA was an amino acid transporter. The ability of the EAAT4 gene product to transport amino acids, and the identity of which amino acids might be transported by this gene product, was assayed in Xenopus oocytes following microinjection of in vitro synthesized EAAT4 RNA.

Briefly, the coding sequence of the EAAT4 cDNA was isolated with unique flanking restriction sites using a PCR-based assay. In this assay, each of the complementary primers used for PCR amplification of the coding sequence contained a sequence encoding a unique restriction enzyme recognition site at the 5' terminus of each PCR primer. For EAAT4 , the sense primer contained a HindIII recognition sequence (A↓AGCTT), and the antisense primer contained an XbaI recognition sequence (T↓CTAGA) at their respective 5' termini. Each of the PCR primers used for amplifying EAAT4 sequences had the following sequence:

EAAT4 sense primer

5'-GCGCGTCGACAAGCTTGCCATGCAACAGCCTGTT-3' (SEQ ID NO:12);

EAAT4 antisense primer

5'-GCGCTCTAGATCAGCCCACGGTCAGTTG-3' (SEQ ID NO:13).

PCR amplification was performed for 30 cycles, each cycle comprising 30 seconds at 94° C., 30 seconds at 55° C. and 1 minute at 72° C. Following the PCR, the product of the amplification reaction was purified using standard techniques (Saiki et al., 1988, Science 239: 487-491). The DNA was then digested with the restriction enzymes HindIII and XbaI and then cloned into the polylinker of an oocyte transcription vector (pOTV; see Arriza et al., 1992, ibid.). Capped RNA was synthesized from linearized plasmid employing bacteriophage T7 RNA polymerase (mMessage mMachine; Ambion, Austin, Tex.), diluted with water to a concentration of 400 μg/mL, and 50 nL of this EAAT4 RNA was injected into defolliculated stage V or VI oocytes. Oocytes were prepared as described (Quick and Lester, 1994, Methods in Neuroscience 19: 261-279) and maintained at 17° C. for up to 5 days.

Amino acid transport in these oocytes was assayed at room temperature 3-5 days post injection using various concentrations of ³ H!-L-aspartate or ³ H!-L-glutamate (obtained from New England Nuclear, Boston, Mass.) in ND96 buffer (96 mM NaCl/2 mM KCl/1.8 mM CaCl₂ /1 mM MgCl₂ /5 mM Hepes, pH 7.5).

Two electrode voltage clamp recordings from EAAT4 -expressing oocytes were performed at room temperature using glass microelectrodes filled with 3M KCl solutions (resistance <1 MΩ) and a Ag/AgCl pellet bath ground or an active bath probe. An Axon GeneClamp 500 amplifier was used with Digidata 1200 interfaces. The pClamp suite of programs (Axon Instruments, Foster City, Calif.) was used to control stimulation parameters, for data acquisition and analysis. MacLab data acquisition software and a MacLab/2e interface (ADI Instruments, Milford, Mass.) were used to record electrophysiological experiments. 3M KCl/agar bridges were used to avoid offset voltages associated with buffer changes. Oocytes were continuously superfused with ND96 or ion substituted ND96 during the recording session.

The properties of EAAT4 cRNA-injected oocytes were examined by analysis of excitatory amino acid-induced currents in voltage-clamped oocytes. In these experiments, the maximum current of depolarization (I_(max)) and the transport constant (K_(m)) induced by treatment with a variety of putative EAAT4 transporter substrates was determined. The results of these experiments are shown in Table I. Injected oocytes were also incubated with a mixture of radiolabeled amino acid ( ³ H!-L-glutamate (17.8 Ci/mmol) or ³ H!-D-aspartate (15.5 Ci/mmol); Dupont-NEN) and non-radiolabeled amino acid at increasing doses of 0.1, 0.3, 1, 3, 10 and 100 μM for 10 min. for determination of the V_(max) and K_(m) of substrate flux. After incubation, the cells were washed four times with ice-cold PBS, solubilized with a solution of 0.1% sodium dodecyl sulfate (SDS) and the amount of radioactivity associated with the cells determined using standard liquid scintillation counting methods.

Application of L-aspartate or L-glutamate to EAAT4 cRNA-injected, voltage-clamped oocytes induced dose-dependent, saturable inward currents; no such currents were observed in control, mock-injected oocytes. Flux experiments showed that oocytes injected with the EAAT4 excitatory amino acid transporter-encoding cRNA accumulated significantly-higher (about 30-fold higher) saturable, sodium-dependent uptake of ³ H!-L-aspartate and ³ H!-L-glutamate than did mock-injected oocytes. The maximal currents elicited by other test compounds were normalized relative to the maximal current obtained with a saturating dose (100 μM) of L-aspartate in the same oocyte such that these determinations were independent of the level of EAAT4 expression in individual oocytes. For this normalization, the current elicited by a maximal dose of L-aspartate was measured before and/or after dose response determinations for each compound and given a normalized I_(max) value of 1.0. No compound tested induced a depolarizing current in uninjected oocytes or water-injected oocytes. The course of uptake of 10 μM radioactive aspartate was found to be linear for at least 20 min in assays performed at room temperature. The K_(m) values derived from the current measurements as well as radiolabel substrate uptake experiments, as shown in Table I, were about 10-fold lower than those found for previously-disclosed members of the EAAT transporter family. Maximal flux and current measurements (Table 1) indicated a discrepancy between the maximal transport and maximal current generated by L-aspartate and L-glutamate. Although L-aspartate produced a current significantly larger than L-glutamate (1.0 versus 0.37, respectively), its maximal transport rate is significantly lower than that of L-glutamate (3.26 versus 5.72). This data suggested that the substrate elicited currents observed are not a direct reflection of substrate transport and that the two phenomena may be uncoupled.

Structural analogues of glutamate, including L-trans-2,4-pyrrolidine dicarboxylic acid, L-quisqualate and L-α-amino adipate, also elicited currents of varying magnitude in EAAT4-injected oocytes, while kainic acid, which blocks glutamate transport in some brain regions, was found to be ineffective in either eliciting a current or blocking an L-aspartate induced current at concentrations as high as 5 mM. These properties of the EAAT4 transporter are consistent with glutamate uptake activity previously reported for cerebellum and are consistent with localization of EAAT4 expression primarily in cerebellar tissues.

Further characterization of the electrophysiology of EAAT4 accompanying aspartate transport revealed a significant difference between EAAT4 and the previously-disclosed members of the EAAT transporter family. L-glutamate- and L-aspartate-induced currents found in voltage-clamped oocytes expressing these other members of the EAAT family exhibited strong inward rectification (i.e., currents were induced that were preferentially inward) and were not found to reverse below +40 mV. In contrast, 10 μM L-aspartate was found to induce an outward current in EAAT4-injected oocytes at voltages more positive than ˜-20 mV. Results of experiments demonstrating this phenomenon are shown in FIG. 6A. In FIG. 6B it is shown that the voltage-dependence of the L-aspartate induced current is approximately linear from about -100 mV to about +40 mV, reversing at -22±1.6 mV (n=18). This value is approximately equal to the previously-reported equilibrium potential of chloride ion in native Xenopus oocytes (-24 mV; see Barish, 1983, J. Physiol. (London) 342: 309-325).

To investigate the significance of this coincidence, the chloride ion-dependence was assayed by substituting chloride ion with gluconate ion. The reversal potential of the L-aspartate induced currents were found to shift by 57±1.5 mV for every ten-fold change in chloride ion concentration, as shown in FIGS. 6B and 6C. This result is in accord with theoretical predictions of the Nernst equation for chloride-ion selective conductance. Similar results were obtained using L-glutamate (reversal potential shifted 50±2 mV for every ten-fold change in chloride ion concentration). The difference in the reversal potential shift seen with L-glutamate and L-aspartate (50 mV versus 57 mV) results from differences in their relative efficacies as transport substrates (Glu>Asp) and as elicitors of the chloride conductance (Asp>Glu).

Complete removal of chloride by substitution with gluconate ion abolished the L-aspartate induced outward currents at depolarized potentials (see FIG. 6B). However, L-aspartate transport at -60 mV in the absence of chloride ion (V_(max) =4.7±0.3 fmol/s, n=8) was not significantly different than transport in the presence of chloride ion (V_(max) =5.9±0.3 fmol/s, n=8), indicating that transport is not dependent on external chloride ion. In contrast, substitution of sodium ions with choline completely and reversibly abolished L-aspartate-induced currents, consistent with the sodium dependence of uptake and with the sodium-dependent activation of chloride conductance by excitatory amino acids (FIG. 6D).

                  TABLE I     ______________________________________     Pharmacological Properties of EAAT4     Substrate Flux and Conductance Currents     ______________________________________     Amino Acid     K.sub.m (μM)                              V.sub.max     ______________________________________      .sup.3 H!-L-aspartate                    0.97 ± 0.29                              3.26 ± 0.06      .sup.3 H!-L-glutamate                    2.49 ± 0.87                              5.72 ± 0.52     ______________________________________     Amino Acid     K.sub.m (μM)                              I.sub.max     ______________________________________     L-aspartate    1.84 ± 0.46                              1.0     L-glutamate    3.3 ± 0.4                              0.37 ± 0.07     D-aspartate    2.5 ± 0.3                              1.0 ± 0.1     L-α-adipate                    168 ± 11                              0.75 ± 0.02     L-quisqualate  99 ± 11                              0.47 ± 0.06     L-homocysteate 403 ± 72                              0.83 ± 0.05     PDC*           2.6 ± 0.4                              0.41 ± 0.01     Kainic acid    >5000     undetectable     ______________________________________      NOTE: data is expressed as the mean of at least 5 determinations ±      standard error.      * = Ltrans-2,4-pyrrolidine dicarboxylic acid

V_(max) was determined by least squares fit to the equation:

    V=V.sub.max ×( S!/(K.sub.m + S!)

where V_(max) is the maximal transport rate and K_(m) is the transport constant

The magnitude of the induced chloride conductance in EAAT4 distinguishes it from EAAT1, EAAT2, or EAAT3. EAAT1 through EAAT3 have large transport currents with small or undetectable chloride conductances, such that their current/voltage profiles show inward rectification, i.e., at positive potentials the current is reduced but is not reversed or outward at potentials less than +40 mV. This is illustrated by the I-V profile for EAAT2 shown in FIG. 7A. In contrast, the EAAT4 I-V profile does not show rectification; rather, the profile is linear with the reversal potential .sup.˜- 20 mV, and the reversal potential is constant regardless of the dose of L-aspartate applied (FIG. 7B). Flux studies under voltage-clamp conditions were conducted and fit to the Faraday equation. It was concluded that greater than 95% of the L-aspartate induced current in EAAT4-expressing oocytes can be attributed to chloride conductance.

L-aspartate and L-glutamate were found to differ in the degree to which they elicit either the transport current component or the chloride conductance component of EAAT4 (FIG. 7C). This is reflected by the fact that, although the reversal potential for L-aspartate was ˜-20 mV, L-glutamate elicited a more robust transport component and therefore its measured reversal potential was ˜-3 mV. Various compounds were tested and a characteristic rank order for reversal potential (more negative to less negative) was found: L-aspartate>PDC>L-α-aminoadipate>L-glutamate>L-quisqualate.

These data demonstrated that the EAAT4 transporter is capable of mediating both 1) the uptake of excitatory amino acids such as glutamate and aspartate, and 2) a substrate-gated increase in chloride conductance. Various substrates can be more or less effective as either amino acid uptake inhibitors or as elicitors of chloride conductance. Thus, the pharmacology of the two functions are separable and therefore subject to selective interventions, i.e., compounds that selectively inhibit or stimulate chloride ion conductance without affecting excitatory amino acid uptake.

The physiological significance of the large chloride conductance of EAAT4 is unknown; but like the chloride conductance gated by GABA-A receptors, it may have a general inhibitory affect on neurotransmission. It may therefore be therapeutically beneficial to selectively stimulate or inhibit the EAAT4 chloride conductance in diseases such as epilepsy, excitotoxicity, and neurodegenerative diseases. The separability of the two biochemical functions of amino acid uptake and chloride ion conductance in the EAAT4 provides an assay for detecting and identifying compounds that inhibit or stimulate the chloride ion conductance of the EAAT4 transporter but do not affect amino acid uptake. Such compounds are advantageous, due to the recognized hazards of pharmaceutical agents that inhibit amino acid uptake in the brain. The assays described herein provide a method for screening for agents that can selectively inhibit or stimulate chloride conductance without the risk of brain injury associated with concommitant inhibition of amino acid uptake.

Briefly, such assays are performed as follows, using voltage-clamped oocytes expressing EAAT4 as described above. First, the compounds are tested for the ability to elicit a current in the voltage-clamped, EAAT4-expressing oocytes. If the compound does not elicit a current, the compound is then co-applied to the oocytes in the presence of L-aspartate to determine whether the compound is an inhibitor of the aspartate-elicited current. If the tested compound elicits a current, the relationship between the elicited current and the voltage is determined (as shown in FIGS. 6 and 7). This analysis yields the relative current amplitude, the reversal potential and the degree of rectification caused by treatment of the oocyte with the test compound. As described above, the reversal potential and degree of rectification reflect the relative contributions of the uptake-elicited current and the chloride conductance in the response of the oocyte to the test compound.

Compounds which elicit a current which is determined to have a significant chloride conductance component are then tested for their effect on excitatory amino acid uptake. Mammalian cells or oocytes are treated with detectably-labeled L-aspartate and L-glutamate in the presence or absence of a compound to be tested. Compounds having little effect on excitatory amino acid uptake, particularly L-glutamate uptake, are thereby advantageously distinguished.

EXAMPLE 4 Construction of Fusion Proteins-Recombinant Expression Constructs for Expression of Immunologically-Active Epitopes of Amino Acid Transporters

The EAAT4 amino acid transporter protein of the invention are expressed as fusion proteins in bacteria to produce immunologically-active epitopes. In these experiments, the amino acid transporter cDNAs of the invention are excised from their respective pOTV-containing constructs and subcloned into a pGEX-2T construct (Pharmacia, Piscataway, N.J.) whereby the coding sequences of the amino acid transporter cDNA is translationally in-frame with sequences encoding glutathione-S-transferase (described in Arriza et al., 1992, J. Neurosci. 12: 4045-4055), termed pGST-EAAT4 constructs. After introduction of the pGST-EAAT4 constructs into bacterial cells (E. coli, strain D5α) using conventional techniques (see Sambrook et al., ibid.), fusion protein expression is induced with isopropyl-1-thio-β-D-galactopyranoside as described (Smith & Johnson, 1988, Gene 67: 31-40) and purified using glutathione-Sepharose 4B (Pharmacia). Antibodies are then raised against the amino acid transporter of the invention by inoculation of rabbits with 300-500 μg of purified fusion protein in Freund's adjuvant (Grand Island Biological Co., Grand Island, N.Y.), said inoculation repeated approximately every 4 weeks. Sera are immunoaffinity-purified on columns of Affi-Gel 15 derivatized with purified fusion protein. After salt elution, such antibodies are neutralized, stabilized with bovine serum albumin at a final concentration of 1 mg/mL, dialyzed against PBS and assayed by immunoblotting using conventional techniques (Harlow & Lane, 1988, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.).

It should be understood that the foregoing disclosure emphasizes certain specific embodiments of the invention and that all modifications or alternatives equivalent thereto are within the spirit and scope of the invention as set forth in the appended claims.

    __________________________________________________________________________     #             SEQUENCE LISTING     - (1) GENERAL INFORMATION:     -    (iii) NUMBER OF SEQUENCES: 13     - (2) INFORMATION FOR SEQ ID NO:1:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 1734 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: cDNA     -     (ix) FEATURE:               (A) NAME/KEY: CDS               (B) LOCATION: 9..1703     -     (ix) FEATURE:               (A) NAME/KEY: 5'UTR               (B) LOCATION: 1..8     -     (ix) FEATURE:               (A) NAME/KEY: 3'UTR               (B) LOCATION: 1704..1734     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:     #CTT CGG GAG AGC GGC      50GC AAC AGC CTG TTC              Met Ser Ser His Gly A - #sn Ser Leu Phe Leu Arg Glu Ser Gly     #        10     - CAG CGG CTG GGC CGG GTG GGC TGG CTG CAG CG - #G CTG CAG GAA AGC CTG       98     Gln Arg Leu Gly Arg Val Gly Trp Leu Gln Ar - #g Leu Gln Glu Ser Leu     # 30     - CAG CAG AGA GCA CTG CGC ACG CGC CTG CGC CT - #G CAG ACC ATG ACC CTC      146     Gln Gln Arg Ala Leu Arg Thr Arg Leu Arg Le - #u Gln Thr Met Thr Leu     #                 45     - GAG CAC GTG CTG CGC TTC CTG CGC CGA AAC GC - #C TTC ATT CTG CTG ACG      194     Glu His Val Leu Arg Phe Leu Arg Arg Asn Al - #a Phe Ile Leu Leu Thr     #             60     - GTC AGC GCC GTG GTC ATT GGG GTC AGC CTG GC - #C TTT GCC CTG CGC CCA      242     Val Ser Ala Val Val Ile Gly Val Ser Leu Al - #a Phe Ala Leu Arg Pro     #         75     - TAT CAG CTC ACC TAC CGC CAG ATC AAG TAC TT - #C TCT TTT CCT GGA GAG      290     Tyr Gln Leu Thr Tyr Arg Gln Ile Lys Tyr Ph - #e Ser Phe Pro Gly Glu     #     90     - CTT CTG ATG AGG ATG CTG CAG ATG CTG GTG TT - #A CCT CTC ATT GTC TCC      338     Leu Leu Met Arg Met Leu Gln Met Leu Val Le - #u Pro Leu Ile Val Ser     #110     - AGC CTG GTC ACA GGT ATG GCA TCC CTG GAC AA - #C AAG GCC ACG GGG CGG      386     Ser Leu Val Thr Gly Met Ala Ser Leu Asp As - #n Lys Ala Thr Gly Arg     #               125     - ATG GGG ATG CGG GCA GCT GTG TAC TAC ATG GT - #G ACC ACC ATC ATC GCG      434     Met Gly Met Arg Ala Ala Val Tyr Tyr Met Va - #l Thr Thr Ile Ile Ala     #           140     - GTC TTC ATC GGC ATC CTC ATG GTC ACC ATC AT - #C CAT CCC GGG AAG GGC      482     Val Phe Ile Gly Ile Leu Met Val Thr Ile Il - #e His Pro Gly Lys Gly     #       155     - TCC AAG GAG GGG CTG CAC CGG GAG GGC CGG AT - #C GAG ACC ATC CCC ACA      530     Ser Lys Glu Gly Leu His Arg Glu Gly Arg Il - #e Glu Thr Ile Pro Thr     #   170     - GCT GAT GCC TTC ATG GAC CTG ATC AGA AAT AT - #G TTT CCA CCA AAC CTT      578     Ala Asp Ala Phe Met Asp Leu Ile Arg Asn Me - #t Phe Pro Pro Asn Leu     175                 1 - #80                 1 - #85                 1 -     #90     - GTG GAG GCC TGC TTC AAA CAG TTC AAG ACG CA - #G TAC AGC ACG AGG GTG      626     Val Glu Ala Cys Phe Lys Gln Phe Lys Thr Gl - #n Tyr Ser Thr Arg Val     #               205     - GTA ACC AGG ACC ATG GTG AGG ACA GAG AAC GG - #G TCT GAG CCG GGT GCC      674     Val Thr Arg Thr Met Val Arg Thr Glu Asn Gl - #y Ser Glu Pro Gly Ala     #           220     - TCC ATG CCT CCT CCA TTC TCA GTG GAG AAC GG - #A ACC AGC TTC CTG GAA      722     Ser Met Pro Pro Pro Phe Ser Val Glu Asn Gl - #y Thr Ser Phe Leu Glu     #       235     - AAT GTC ACT CGG GCC TTG GGT ACC CTG CAG GA - #G ATG CTG AGC TTT GAG      770     Asn Val Thr Arg Ala Leu Gly Thr Leu Gln Gl - #u Met Leu Ser Phe Glu     #   250     - GAG ACT GTA CCC GTG CCT GGC TCC GCC AAT GG - #C ATC AAC GCC CTG GGC      818     Glu Thr Val Pro Val Pro Gly Ser Ala Asn Gl - #y Ile Asn Ala Leu Gly     255                 2 - #60                 2 - #65                 2 -     #70     - CTC GTG GTC TTC TCT GTG GCC TTT GGG CTG GT - #C ATT GGT GGC ATG AAA      866     Leu Val Val Phe Ser Val Ala Phe Gly Leu Va - #l Ile Gly Gly Met Lys     #               285     - CAC AAG GGC AGA GTC CTC AGG GAC TTC TTC GA - #C AGC CTC AAT GAG GCT      914     His Lys Gly Arg Val Leu Arg Asp Phe Phe As - #p Ser Leu Asn Glu Ala     #           300     - ATT ATG AGG CTG GTG GGC ATC ATT ATC TGG TA - #T GCA CCT GTG GGC ATC      962     Ile Met Arg Leu Val Gly Ile Ile Ile Trp Ty - #r Ala Pro Val Gly Ile     #       315     - CTG TTC CTG ATT GCT GGG AAG ATT CTG GAG AT - #G GAA GAC ATG GCC GTC     1010     Leu Phe Leu Ile Ala Gly Lys Ile Leu Glu Me - #t Glu Asp Met Ala Val     #   330     - CTG GGG GGT CAG CTG GGC ATG TAC ACC CTG AC - #C GTC ATC GTG GGC CTG     1058     Leu Gly Gly Gln Leu Gly Met Tyr Thr Leu Th - #r Val Ile Val Gly Leu     335                 3 - #40                 3 - #45                 3 -     #50     - TTC CTC CAT GCC GGC ATT GTC CTT CCC CTC AT - #C TAC TTC CTC GTC ACT     1106     Phe Leu His Ala Gly Ile Val Leu Pro Leu Il - #e Tyr Phe Leu Val Thr     #               365     - CAC CGG AAC CCC TTC CCC TTC ATT GGG GGC AT - #G CTA CAA GCC CTC ATC     1154     His Arg Asn Pro Phe Pro Phe Ile Gly Gly Me - #t Leu Gln Ala Leu Ile     #           380     - ACC GCT ATG GGC ACG TCT TCC AGC TCG GCA AC - #G CTG CCC ATC ACC TTC     1202     Thr Ala Met Gly Thr Ser Ser Ser Ser Ala Th - #r Leu Pro Ile Thr Phe     #       395     - CGC TGC CTG GAG GAG GGC CTG GGT GTG GAC CG - #C CGC ATC ACC AGG TTC     1250     Arg Cys Leu Glu Glu Gly Leu Gly Val Asp Ar - #g Arg Ile Thr Arg Phe     #   410     - GTC CTG CCC GTG GGC GCC ACG GTC AAC ATG GA - #T GGC ACT GCC CTC TAC     1298     Val Leu Pro Val Gly Ala Thr Val Asn Met As - #p Gly Thr Ala Leu Tyr     415                 4 - #20                 4 - #25                 4 -     #30     - GAG GCC CTG GCT GCC ATC TTC ATT GCT CAA GT - #T AAC AAC TAC GAG CTC     1346     Glu Ala Leu Ala Ala Ile Phe Ile Ala Gln Va - #l Asn Asn Tyr Glu Leu     #               445     - AAC CTG GGT CAG ATC ACA ACC ATC AGC ATC AC - #G GCC ACA GCA GCC AGT     1394     Asn Leu Gly Gln Ile Thr Thr Ile Ser Ile Th - #r Ala Thr Ala Ala Ser     #           460     - GTT GGG GCT GCT GGC ATC CCC CAG GCG GGT CT - #G GTC ACC ATG GTC ATT     1442     Val Gly Ala Ala Gly Ile Pro Gln Ala Gly Le - #u Val Thr Met Val Ile     #       475     - GTG CTT ACG TCG GTC GGC TTG CCC ACG GAA GA - #C ATC ACG CTC ATC ATC     1490     Val Leu Thr Ser Val Gly Leu Pro Thr Glu As - #p Ile Thr Leu Ile Ile     #   490     - GCC GTG GAC TGG TTC CTT GAC CGG CTT CGC AC - #A ATG ACC AAC GTA CTG     1538     Ala Val Asp Trp Phe Leu Asp Arg Leu Arg Th - #r Met Thr Asn Val Leu     495                 5 - #00                 5 - #05                 5 -     #10     - GGC CAC TCA ATT GGA GCG GCC GTC ATC GAG CA - #C TTG TCT CAG CGG GAG     1586     Gly His Ser Ile Gly Ala Ala Val Ile Glu Hi - #s Leu Ser Gln Arg Glu     #               525     - CTG GAG CTT CAG GAA GCT GAG CTT ACC CTC CC - #C AGC CTG GGG AAA CCC     1634     Leu Glu Leu Gln Glu Ala Glu Leu Thr Leu Pr - #o Ser Leu Gly Lys Pro     #           540     - TAC AAG TCC CTC ATG GCA CAG GAG AAG GGG GC - #A TCC CGG GGA CGG GGA     1682     Tyr Lys Ser Leu Met Ala Gln Glu Lys Gly Al - #a Ser Arg Gly Arg Gly     #       555     - GGC AAC GAG AGT GCT ATG TGAGGGGCCT CCAGCTCTGC CC - #CCCCAGAG AGGA     1734     Gly Asn Glu Ser Ala Met     #   565     - (2) INFORMATION FOR SEQ ID NO:2:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 564 amino               (B) TYPE: amino acid               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: protein     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:     - Met Ser Ser His Gly Asn Ser Leu Phe Leu Ar - #g Glu Ser Gly Gln Arg     #                 15     - Leu Gly Arg Val Gly Trp Leu Gln Arg Leu Gl - #n Glu Ser Leu Gln Gln     #             30     - Arg Ala Leu Arg Thr Arg Leu Arg Leu Gln Th - #r Met Thr Leu Glu His     #         45     - Val Leu Arg Phe Leu Arg Arg Asn Ala Phe Il - #e Leu Leu Thr Val Ser     #     60     - Ala Val Val Ile Gly Val Ser Leu Ala Phe Al - #a Leu Arg Pro Tyr Gln     # 80     - Leu Thr Tyr Arg Gln Ile Lys Tyr Phe Ser Ph - #e Pro Gly Glu Leu Leu     #                 95     - Met Arg Met Leu Gln Met Leu Val Leu Pro Le - #u Ile Val Ser Ser Leu     #           110     - Val Thr Gly Met Ala Ser Leu Asp Asn Lys Al - #a Thr Gly Arg Met Gly     #       125     - Met Arg Ala Ala Val Tyr Tyr Met Val Thr Th - #r Ile Ile Ala Val Phe     #   140     - Ile Gly Ile Leu Met Val Thr Ile Ile His Pr - #o Gly Lys Gly Ser Lys     145                 1 - #50                 1 - #55                 1 -     #60     - Glu Gly Leu His Arg Glu Gly Arg Ile Glu Th - #r Ile Pro Thr Ala Asp     #               175     - Ala Phe Met Asp Leu Ile Arg Asn Met Phe Pr - #o Pro Asn Leu Val Glu     #           190     - Ala Cys Phe Lys Gln Phe Lys Thr Gln Tyr Se - #r Thr Arg Val Val Thr     #       205     - Arg Thr Met Val Arg Thr Glu Asn Gly Ser Gl - #u Pro Gly Ala Ser Met     #   220     - Pro Pro Pro Phe Ser Val Glu Asn Gly Thr Se - #r Phe Leu Glu Asn Val     225                 2 - #30                 2 - #35                 2 -     #40     - Thr Arg Ala Leu Gly Thr Leu Gln Glu Met Le - #u Ser Phe Glu Glu Thr     #               255     - Val Pro Val Pro Gly Ser Ala Asn Gly Ile As - #n Ala Leu Gly Leu Val     #           270     - Val Phe Ser Val Ala Phe Gly Leu Val Ile Gl - #y Gly Met Lys His Lys     #       285     - Gly Arg Val Leu Arg Asp Phe Phe Asp Ser Le - #u Asn Glu Ala Ile Met     #   300     - Arg Leu Val Gly Ile Ile Ile Trp Tyr Ala Pr - #o Val Gly Ile Leu Phe     305                 3 - #10                 3 - #15                 3 -     #20     - Leu Ile Ala Gly Lys Ile Leu Glu Met Glu As - #p Met Ala Val Leu Gly     #               335     - Gly Gln Leu Gly Met Tyr Thr Leu Thr Val Il - #e Val Gly Leu Phe Leu     #           350     - His Ala Gly Ile Val Leu Pro Leu Ile Tyr Ph - #e Leu Val Thr His Arg     #       365     - Asn Pro Phe Pro Phe Ile Gly Gly Met Leu Gl - #n Ala Leu Ile Thr Ala     #   380     - Met Gly Thr Ser Ser Ser Ser Ala Thr Leu Pr - #o Ile Thr Phe Arg Cys     385                 3 - #90                 3 - #95                 4 -     #00     - Leu Glu Glu Gly Leu Gly Val Asp Arg Arg Il - #e Thr Arg Phe Val Leu     #               415     - Pro Val Gly Ala Thr Val Asn Met Asp Gly Th - #r Ala Leu Tyr Glu Ala     #           430     - Leu Ala Ala Ile Phe Ile Ala Gln Val Asn As - #n Tyr Glu Leu Asn Leu     #       445     - Gly Gln Ile Thr Thr Ile Ser Ile Thr Ala Th - #r Ala Ala Ser Val Gly     #   460     - Ala Ala Gly Ile Pro Gln Ala Gly Leu Val Th - #r Met Val Ile Val Leu     465                 4 - #70                 4 - #75                 4 -     #80     - Thr Ser Val Gly Leu Pro Thr Glu Asp Ile Th - #r Leu Ile Ile Ala Val     #               495     - Asp Trp Phe Leu Asp Arg Leu Arg Thr Met Th - #r Asn Val Leu Gly His     #           510     - Ser Ile Gly Ala Ala Val Ile Glu His Leu Se - #r Gln Arg Glu Leu Glu     #       525     - Leu Gln Glu Ala Glu Leu Thr Leu Pro Ser Le - #u Gly Lys Pro Tyr Lys     #   540     - Ser Leu Met Ala Gln Glu Lys Gly Ala Ser Ar - #g Gly Arg Gly Gly Asn     545                 5 - #50                 5 - #55                 5 -     #60     - Glu Ser Ala Met     - (2) INFORMATION FOR SEQ ID NO:3:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 1680 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: cDNA     -     (ix) FEATURE:               (A) NAME/KEY: 5'UTR               (B) LOCATION: 1..30     -     (ix) FEATURE:               (A) NAME/KEY: CDS               (B) LOCATION: 31..1656     -     (ix) FEATURE:               (A) NAME/KEY: 3'UTR               (B) LOCATION: 1657..1680     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:     - AAAGAAGAGA CCCTCCTAGA AAAGTAAAAT ATG ACT AAA AGC AA - #T GGA GAA GAG       54     #Lys Ser Asn Gly Glu Glu     #              5  1     - CCC AAG ATG GGG GGC AGG ATG GAG AGA TTC CA - #G CAG GGA GTC CGT AAA      102     Pro Lys Met Gly Gly Arg Met Glu Arg Phe Gl - #n Gln Gly Val Arg Lys     #     20     - CGC ACA CTT TTG GCC AAG AAG AAA GTG CAG AA - #C ATT ACA AAG GAG GTT      150     Arg Thr Leu Leu Ala Lys Lys Lys Val Gln As - #n Ile Thr Lys Glu Val     # 40     - GTT AAA AGT TAC CTG TTT CGG AAT GCT TTT GT - #G CTG CTC ACA GTC ACC      198     Val Lys Ser Tyr Leu Phe Arg Asn Ala Phe Va - #l Leu Leu Thr Val Thr     #                 55     - GCT GTC ATT GTG GGT ACA ATC CTT GGA TTT AC - #C CTC CGA CCA TAC AGA      246     Ala Val Ile Val Gly Thr Ile Leu Gly Phe Th - #r Leu Arg Pro Tyr Arg     #             70     - ATG AGC TAC CGG GAA GTC AAG TAC TTC TCC TT - #T CCT GGG GAA CTT CTG      294     Met Ser Tyr Arg Glu Val Lys Tyr Phe Ser Ph - #e Pro Gly Glu Leu Leu     #         85     - ATG AGG ATG TTA CAG ATG CTG GTC TTA CCA CT - #T ATC ATC TCC AGT CTT      342     Met Arg Met Leu Gln Met Leu Val Leu Pro Le - #u Ile Ile Ser Ser Leu     #    100     - GTC ACA GGA ATG GCG GCG CTA GAT AGT AAG GC - #A TCA GGG AAG TGG GAA      390     Val Thr Gly Met Ala Ala Leu Asp Ser Lys Al - #a Ser Gly Lys Trp Glu     105                 1 - #10                 1 - #15                 1 -     #20     - TGC GGA GCT GTA GTC TAT TAT ATG ACT ACC AC - #C ATC ATT GCT GTG GTG      438     Cys Gly Ala Val Val Tyr Tyr Met Thr Thr Th - #r Ile Ile Ala Val Val     #               135     - ATT GGC ATA ATC ATT GTC ATC ATC ATC CAT CC - #T GGG AAG GGC ACA AAG      486     Ile Gly Ile Ile Ile Val Ile Ile Ile His Pr - #o Gly Lys Gly Thr Lys     #           150     - GAA AAC ATG CAC AGA GAA GGC AAA ATT GTA CG - #A GTG ACA GCT GCA GAT      534     Glu Asn Met His Arg Glu Gly Lys Ile Val Ar - #g Val Thr Ala Ala Asp     #       165     - GCC TTC CTG GAC TTG ATC AGG AAC ATG TTA AA - #T CCA AAT CTG GTA GAA      582     Ala Phe Leu Asp Leu Ile Arg Asn Met Leu As - #n Pro Asn Leu Val Glu     #   180     - GCC TGC TTT AAA CAG TTT AAA ACC AAC TAT GA - #G AAG AGA AGC TTT AAA      630     Ala Cys Phe Lys Gln Phe Lys Thr Asn Tyr Gl - #u Lys Arg Ser Phe Lys     185                 1 - #90                 1 - #95                 2 -     #00     - GTG CCC ATC CAG GCC AAC GAA ACG CTT GTG GG - #T GCT GTG ATA AAC AAT      678     Val Pro Ile Gln Ala Asn Glu Thr Leu Val Gl - #y Ala Val Ile Asn Asn     #               215     - GTG TCT GAG GCC ATG GAG ACT CTT ACC CGA AT - #C ACA GAG GAG CTG GTC      726     Val Ser Glu Ala Met Glu Thr Leu Thr Arg Il - #e Thr Glu Glu Leu Val     #           230     - CCA GTT CCA GGA TCT GTG AAT GGA GTC AAT GC - #C CTG GGT CTA GTT GTC      774     Pro Val Pro Gly Ser Val Asn Gly Val Asn Al - #a Leu Gly Leu Val Val     #       245     - TTC TCC ATG TGC TTC GGT TTT GTG ATT GGA AA - #C ATG AAG GAA CAG GGG      822     Phe Ser Met Cys Phe Gly Phe Val Ile Gly As - #n Met Lys Glu Gln Gly     #   260     - CAG GCC CTG AGA GAG TTC TTT GAT TCT CTT AA - #C GAA GCC ATC ATG AGA      870     Gln Ala Leu Arg Glu Phe Phe Asp Ser Leu As - #n Glu Ala Ile Met Arg     265                 2 - #70                 2 - #75                 2 -     #80     - CTG GTA GCA GTA ATA ATG TGG TAT GCC CCC GT - #G GGT ATT CTC TTC CTG      918     Leu Val Ala Val Ile Met Trp Tyr Ala Pro Va - #l Gly Ile Leu Phe Leu     #               295     - ATT GCT GGG AAG ATT GTG GAG ATG GAA GAC AT - #G GGT GTG ATT GGG GGG      966     Ile Ala Gly Lys Ile Val Glu Met Glu Asp Me - #t Gly Val Ile Gly Gly     #           310     - CAG CTT GCC ATG TAC ACC GTG ACT GTC ATT GT - #T GGC TTA CTC ATT CAC     1014     Gln Leu Ala Met Tyr Thr Val Thr Val Ile Va - #l Gly Leu Leu Ile His     #       325     - GCA GTC ATC GTC TTG CCA CTC CTC TAC TTC TT - #G GTA ACA CGG AAA AAC     1062     Ala Val Ile Val Leu Pro Leu Leu Tyr Phe Le - #u Val Thr Arg Lys Asn     #   340     - CCT TGG GTT TTT ATT GGA GGG TTG CTG CAA GC - #A CTC ATC ACC GCT CTG     1110     Pro Trp Val Phe Ile Gly Gly Leu Leu Gln Al - #a Leu Ile Thr Ala Leu     345                 3 - #50                 3 - #55                 3 -     #60     - GGG ACC TCT TCA AGT TCT GCC ACC CTA CCC AT - #C ACC TTC AAG TGC CTG     1158     Gly Thr Ser Ser Ser Ser Ala Thr Leu Pro Il - #e Thr Phe Lys Cys Leu     #               375     - GAA GAG AAC AAT GGC GTG GAC AAG CGC GTC AC - #C AGA TTC GTG CTC CCC     1206     Glu Glu Asn Asn Gly Val Asp Lys Arg Val Th - #r Arg Phe Val Leu Pro     #           390     - GTA GGA GCC ACC ATT AAC ATG GAT GGG ACT GC - #C CTC TAT GAG GCT TTG     1254     Val Gly Ala Thr Ile Asn Met Asp Gly Thr Al - #a Leu Tyr Glu Ala Leu     #       405     - GCT GCC ATT TTC ATT GCT CAA GTT AAC AAC TT - #T GAA CTG AAC TTC GGA     1302     Ala Ala Ile Phe Ile Ala Gln Val Asn Asn Ph - #e Glu Leu Asn Phe Gly     #   420     - CAA ATT ATT ACA ATC AGC ATC ACA GCC ACA GC - #T GCC AGT ATT GGG GCA     1350     Gln Ile Ile Thr Ile Ser Ile Thr Ala Thr Al - #a Ala Ser Ile Gly Ala     425                 4 - #30                 4 - #35                 4 -     #40     - GCT GGA ATT CCT CAG GCG GGC CTG GTC ACT AT - #G GTC ATT GTG CTG ACA     1398     Ala Gly Ile Pro Gln Ala Gly Leu Val Thr Me - #t Val Ile Val Leu Thr     #               455     - TCT GTC GGC CTG CCC ACT GAC GAC ATC ACG CT - #C ATC ATC GCG GTG GAC     1446     Ser Val Gly Leu Pro Thr Asp Asp Ile Thr Le - #u Ile Ile Ala Val Asp     #           470     - TGG TTC TTG GAT CGC CTC CGG ACC ACC ACC AA - #C GTA CTG GGA GAC TCC     1494     Trp Phe Leu Asp Arg Leu Arg Thr Thr Thr As - #n Val Leu Gly Asp Ser     #       485     - CTG GGA GCT GGG ATT GTG GAG CAC TTG TCA CG - #A CAT GAA CTG AAG AAC     1542     Leu Gly Ala Gly Ile Val Glu His Leu Ser Ar - #g His Glu Leu Lys Asn     #   500     - AGA GAT GTT GAA ATG GGT AAC TCA GTG ATT GA - #A GAG AAT GAA ATG AAG     1590     Arg Asp Val Glu Met Gly Asn Ser Val Ile Gl - #u Glu Asn Glu Met Lys     505                 5 - #10                 5 - #15                 5 -     #20     - AAA CCA TAT CAA CTG ATT GCA CAG GAC AAT GA - #A ACT GAG AAA CCC ATC     1638     Lys Pro Tyr Gln Leu Ile Ala Gln Asp Asn Gl - #u Thr Glu Lys Pro Ile     #               535     - GAC AGT GAA ACC AAG ATG TAGACTAACA TAAAGAAACA CT - #TT     #1680     Asp Ser Glu Thr Lys Met                 540     - (2) INFORMATION FOR SEQ ID NO:4:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 542 amino               (B) TYPE: amino acid               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: protein     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:     - Met Thr Lys Ser Asn Gly Glu Glu Pro Lys Me - #t Gly Gly Arg Met Glu     #                 15     - Arg Phe Gln Gln Gly Val Arg Lys Arg Thr Le - #u Leu Ala Lys Lys Lys     #             30     - Val Gln Asn Ile Thr Lys Glu Val Val Lys Se - #r Tyr Leu Phe Arg Asn     #         45     - Ala Phe Val Leu Leu Thr Val Thr Ala Val Il - #e Val Gly Thr Ile Leu     #     60     - Gly Phe Thr Leu Arg Pro Tyr Arg Met Ser Ty - #r Arg Glu Val Lys Tyr     # 80     - Phe Ser Phe Pro Gly Glu Leu Leu Met Arg Me - #t Leu Gln Met Leu Val     #                 95     - Leu Pro Leu Ile Ile Ser Ser Leu Val Thr Gl - #y Met Ala Ala Leu Asp     #           110     - Ser Lys Ala Ser Gly Lys Trp Glu Cys Gly Al - #a Val Val Tyr Tyr Met     #       125     - Thr Thr Thr Ile Ile Ala Val Val Ile Gly Il - #e Ile Ile Val Ile Ile     #   140     - Ile His Pro Gly Lys Gly Thr Lys Glu Asn Me - #t His Arg Glu Gly Lys     145                 1 - #50                 1 - #55                 1 -     #60     - Ile Val Arg Val Thr Ala Ala Asp Ala Phe Le - #u Asp Leu Ile Arg Asn     #               175     - Met Leu Asn Pro Asn Leu Val Glu Ala Cys Ph - #e Lys Gln Phe Lys Thr     #           190     - Asn Tyr Glu Lys Arg Ser Phe Lys Val Pro Il - #e Gln Ala Asn Glu Thr     #       205     - Leu Val Gly Ala Val Ile Asn Asn Val Ser Gl - #u Ala Met Glu Thr Leu     #   220     - Thr Arg Ile Thr Glu Glu Leu Val Pro Val Pr - #o Gly Ser Val Asn Gly     225                 2 - #30                 2 - #35                 2 -     #40     - Val Asn Ala Leu Gly Leu Val Val Phe Ser Me - #t Cys Phe Gly Phe Val     #               255     - Ile Gly Asn Met Lys Glu Gln Gly Gln Ala Le - #u Arg Glu Phe Phe Asp     #           270     - Ser Leu Asn Glu Ala Ile Met Arg Leu Val Al - #a Val Ile Met Trp Tyr     #       285     - Ala Pro Val Gly Ile Leu Phe Leu Ile Ala Gl - #y Lys Ile Val Glu Met     #   300     - Glu Asp Met Gly Val Ile Gly Gly Gln Leu Al - #a Met Tyr Thr Val Thr     305                 3 - #10                 3 - #15                 3 -     #20     - Val Ile Val Gly Leu Leu Ile His Ala Val Il - #e Val Leu Pro Leu Leu     #               335     - Tyr Phe Leu Val Thr Arg Lys Asn Pro Trp Va - #l Phe Ile Gly Gly Leu     #           350     - Leu Gln Ala Leu Ile Thr Ala Leu Gly Thr Se - #r Ser Ser Ser Ala Thr     #       365     - Leu Pro Ile Thr Phe Lys Cys Leu Glu Glu As - #n Asn Gly Val Asp Lys     #   380     - Arg Val Thr Arg Phe Val Leu Pro Val Gly Al - #a Thr Ile Asn Met Asp     385                 3 - #90                 3 - #95                 4 -     #00     - Gly Thr Ala Leu Tyr Glu Ala Leu Ala Ala Il - #e Phe Ile Ala Gln Val     #               415     - Asn Asn Phe Glu Leu Asn Phe Gly Gln Ile Il - #e Thr Ile Ser Ile Thr     #           430     - Ala Thr Ala Ala Ser Ile Gly Ala Ala Gly Il - #e Pro Gln Ala Gly Leu     #       445     - Val Thr Met Val Ile Val Leu Thr Ser Val Gl - #y Leu Pro Thr Asp Asp     #   460     - Ile Thr Leu Ile Ile Ala Val Asp Trp Phe Le - #u Asp Arg Leu Arg Thr     465                 4 - #70                 4 - #75                 4 -     #80     - Thr Thr Asn Val Leu Gly Asp Ser Leu Gly Al - #a Gly Ile Val Glu His     #               495     - Leu Ser Arg His Glu Leu Lys Asn Arg Asp Va - #l Glu Met Gly Asn Ser     #           510     - Val Ile Glu Glu Asn Glu Met Lys Lys Pro Ty - #r Gln Leu Ile Ala Gln     #       525     - Asp Asn Glu Thr Glu Lys Pro Ile Asp Ser Gl - #u Thr Lys Met     #   540     - (2) INFORMATION FOR SEQ ID NO:5:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 1800 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: cDNA     -     (ix) FEATURE:               (A) NAME/KEY: 5'UTR               (B) LOCATION: 1..33     -     (ix) FEATURE:               (A) NAME/KEY: CDS               (B) LOCATION: 34..1755       (ix) FEATURE:               (A) NAME/KEY: 3'UTR               (B) LOCATION: 1756..1800     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:     - GATAGTGCTG AAGAGGAGGG GCGTTCCCAG ACC ATG GCA TCT AC - #G GAA GGT GCC       54     # Met Ala Ser Thr Glu Gly Ala     #5  1     - AAC AAT ATG CCC AAG CAG GTG GAA GTG CGA AT - #G CCA GAC AGT CAT CTT      102     Asn Asn Met Pro Lys Gln Val Glu Val Arg Me - #t Pro Asp Ser His Leu     #         20     - GGC TCA GAG GAA CCC AAG CAC CGG CAC CTG GG - #C CTG CGC CTG TGT GAC      150     Gly Ser Glu Glu Pro Lys His Arg His Leu Gl - #y Leu Arg Leu Cys Asp     #     35     - AAG CTG GGG AAG AAT CTG CTG CTC ACC CTG AC - #G GTG TTT GGT GTC ATC      198     Lys Leu Gly Lys Asn Leu Leu Leu Thr Leu Th - #r Val Phe Gly Val Ile     # 55     - CTG GGA GCA GTG TGT GGA GGG CTT CTT CGC TT - #G GCA TCT CCC ATC CAC      246     Leu Gly Ala Val Cys Gly Gly Leu Leu Arg Le - #u Ala Ser Pro Ile His     #                 70     - CCT GAT GTG GTT ATG TTA ATA GCC TTC CCA GG - #G GAT ATA CTC ATG AGG      294     Pro Asp Val Val Met Leu Ile Ala Phe Pro Gl - #y Asp Ile Leu Met Arg     #             85     - ATG CTA AAA ATG CTC ATT CTG GGT CTA ATC AT - #C TCC AGC TTA ATC ACA      342     Met Leu Lys Met Leu Ile Leu Gly Leu Ile Il - #e Ser Ser Leu Ile Thr     #        100     - GGG TTG TCA GGC CTG GAT GCT AAG GCT AGT GG - #C CGC TTG GGC ACG AGA      390     Gly Leu Ser Gly Leu Asp Ala Lys Ala Ser Gl - #y Arg Leu Gly Thr Arg     #   115     - GCC ATG GTG TAT TAC ATG TCC ACG ACC ATC AT - #T GCT GCA GTA CTG GGG      438     Ala Met Val Tyr Tyr Met Ser Thr Thr Ile Il - #e Ala Ala Val Leu Gly     120                 1 - #25                 1 - #30                 1 -     #35     - GTC ATT CTG GTC TTG GCT ATC CAT CCA GGC AA - #T CCC AAG CTC AAG AAG      486     Val Ile Leu Val Leu Ala Ile His Pro Gly As - #n Pro Lys Leu Lys Lys     #               150     - CAG CTG GGG CCT GGG AAG AAG AAT GAT GAA GT - #G TCC AGC CTG GAT GCC      534     Gln Leu Gly Pro Gly Lys Lys Asn Asp Glu Va - #l Ser Ser Leu Asp Ala     #           165     - TTC CTG GAC CTT ATT CGA AAT CTC TTC CCT GA - #A AAC CTT GTC CAA GCC      582     Phe Leu Asp Leu Ile Arg Asn Leu Phe Pro Gl - #u Asn Leu Val Gln Ala     #       180     - TGC TTT CAA CAG ATT CAA ACA GTG ACG AAG AA - #A GTC CTG GTT GCA CCA      630     Cys Phe Gln Gln Ile Gln Thr Val Thr Lys Ly - #s Val Leu Val Ala Pro     #   195     - CCG CCA GAC GAG GAG GCC AAC GCA ACC AGC GC - #T GAA GTC TCT CTG TTG      678     Pro Pro Asp Glu Glu Ala Asn Ala Thr Ser Al - #a Glu Val Ser Leu Leu     200                 2 - #05                 2 - #10                 2 -     #15     - AAC GAG ACT GTG ACT GAG GTG CCG GAG GAG AC - #T AAG ATG GTT ATC AAG      726     Asn Glu Thr Val Thr Glu Val Pro Glu Glu Th - #r Lys Met Val Ile Lys     #               230     - AAG GGC CTG GAG TTC AAG GAT GGG ATG AAC GT - #C TTA GGT CTG ATA GGG      774     Lys Gly Leu Glu Phe Lys Asp Gly Met Asn Va - #l Leu Gly Leu Ile Gly     #           245     - TTT TTC ATT GCT TTT GGC ATC GCT ATG GGG AA - #G ATG GGA GAT CAG GCC      822     Phe Phe Ile Ala Phe Gly Ile Ala Met Gly Ly - #s Met Gly Asp Gln Ala     #       260     - AAG CTG ATG GTG GAT TTC TTC AAC ATT TTG AA - #T GAG ATT GTA ATG AAG      870     Lys Leu Met Val Asp Phe Phe Asn Ile Leu As - #n Glu Ile Val Met Lys     #   275     - TTA GTG ATC ATG ATC ATG TGG TAC TCT CCC CT - #G GGT ATC GCC TGC CTG      918     Leu Val Ile Met Ile Met Trp Tyr Ser Pro Le - #u Gly Ile Ala Cys Leu     280                 2 - #85                 2 - #90                 2 -     #95     - ATC TGT GGA AAG ATC ATT GCA ATC AAG GAC TT - #A GAA GTG GTT GCT AGG      966     Ile Cys Gly Lys Ile Ile Ala Ile Lys Asp Le - #u Glu Val Val Ala Arg     #               310     - CAA CTG GGG ATG TAC ATG GTA ACA GTG ATC AT - #A GGC CTC ATC ATC CAC     1014     Gln Leu Gly Met Tyr Met Val Thr Val Ile Il - #e Gly Leu Ile Ile His     #           325     - GGG GGC ATC TTT CTC CCC TTG ATT TAC TTT GT - #A GTG ACC AGG AAA AAC     1062     Gly Gly Ile Phe Leu Pro Leu Ile Tyr Phe Va - #l Val Thr Arg Lys Asn     #       340     - CCC TTC TCC CTT TTT GCT GGC ATT TTC CAA GC - #T TGG ATC ACT GCC CTG     1110     Pro Phe Ser Leu Phe Ala Gly Ile Phe Gln Al - #a Trp Ile Thr Ala Leu     #   355     - GGC ACC GCT TCC AGT GCT GGA ACT TTG CCT GT - #C ACC TTT CGT TGC CTG     1158     Gly Thr Ala Ser Ser Ala Gly Thr Leu Pro Va - #l Thr Phe Arg Cys Leu     360                 3 - #65                 3 - #70                 3 -     #75     - GAA GAA AAT CTG GGG ATT GAT AAG CGT GTG AC - #T AGA TTC GTC CTT CCT     1206     Glu Glu Asn Leu Gly Ile Asp Lys Arg Val Th - #r Arg Phe Val Leu Pro     #               390     - GTT GGA GCA ACC ATT AAC ATG GAT GGT ACA GC - #C CTT TAT GAA GCG GTG     1254     Val Gly Ala Thr Ile Asn Met Asp Gly Thr Al - #a Leu Tyr Glu Ala Val     #           405     - GCC GCC ATC TTT ATA GCC CAA ATG AAT GGT GT - #T GTC CTG GAT GGA GGA     1302     Ala Ala Ile Phe Ile Ala Gln Met Asn Gly Va - #l Val Leu Asp Gly Gly     #       420     - CAG ATT GTG ACT GTA AGC CTC ACA GCC ACC CT - #G GCA AGC GTC GGC GCG     1350     Gln Ile Val Thr Val Ser Leu Thr Ala Thr Le - #u Ala Ser Val Gly Ala     #   435     - GCC AGT ATC CCC AGT GCC GGG CTG GTC ACC AT - #G CTC CTC ATT CTG ACA     1398     Ala Ser Ile Pro Ser Ala Gly Leu Val Thr Me - #t Leu Leu Ile Leu Thr     440                 4 - #45                 4 - #50                 4 -     #55     - GCC GTG GGC CTG CCA ACA GAG GAC ATC AGC TT - #G CTG GTG GCT GTG GAC     1446     Ala Val Gly Leu Pro Thr Glu Asp Ile Ser Le - #u Leu Val Ala Val Asp     #               470     - TGG CTG CTG GAC AGG ATG AGA ACT TCA GTC AA - #T GTT GTG GGT GAC TCT     1494     Trp Leu Leu Asp Arg Met Arg Thr Ser Val As - #n Val Val Gly Asp Ser     #           485     - TTT GGG GCT GGG ATA GTC TAT CAC CTC TCC AA - #G TCT GAG CTG GAT ACC     1542     Phe Gly Ala Gly Ile Val Tyr His Leu Ser Ly - #s Ser Glu Leu Asp Thr     #       500     - ATT GAC TCC CAG CAT CGA GTG CAT GAA GAT AT - #T GAA ATG ACC AAG ACT     1590     Ile Asp Ser Gln His Arg Val His Glu Asp Il - #e Glu Met Thr Lys Thr     #   515     - CAA TCC ATT TAT GAT GAC ATG AAG AAC CAC AG - #G GAA AGC AAC TCT AAT     1638     Gln Ser Ile Tyr Asp Asp Met Lys Asn His Ar - #g Glu Ser Asn Ser Asn     520                 5 - #25                 5 - #30                 5 -     #35     - CAA TGT GTC TAT GCT GCA CAC AAC TCT GTC AT - #A GTA GAT GAA TGC AAG     1686     Gln Cys Val Tyr Ala Ala His Asn Ser Val Il - #e Val Asp Glu Cys Lys     #               550     - GTA ACT CTG GCA GCC AAT GGA AAG TCA GCC GA - #C TGC AGT GTT GAG GAA     1734     Val Thr Leu Ala Ala Asn Gly Lys Ser Ala As - #p Cys Ser Val Glu Glu     #           565     - GAA CCT TGG AAA CGT GAG AAA TAAGGATATG AGTCTCAGC - #A AATTCTTGAA     1785     Glu Pro Trp Lys Arg Glu Lys             570     #  1800     - (2) INFORMATION FOR SEQ ID NO:6:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 574 amino               (B) TYPE: amino acid               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: protein     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:     - Met Ala Ser Thr Glu Gly Ala Asn Asn Met Pr - #o Lys Gln Val Glu Val     #                 15     - Arg Met Pro Asp Ser His Leu Gly Ser Glu Gl - #u Pro Lys His Arg His     #             30     - Leu Gly Leu Arg Leu Cys Asp Lys Leu Gly Ly - #s Asn Leu Leu Leu Thr     #         45     - Leu Thr Val Phe Gly Val Ile Leu Gly Ala Va - #l Cys Gly Gly Leu Leu     #     60     - Arg Leu Ala Ser Pro Ile His Pro Asp Val Va - #l Met Leu Ile Ala Phe     # 80     - Pro Gly Asp Ile Leu Met Arg Met Leu Lys Me - #t Leu Ile Leu Gly Leu     #                 95     - Ile Ile Ser Ser Leu Ile Thr Gly Leu Ser Gl - #y Leu Asp Ala Lys Ala     #           110     - Ser Gly Arg Leu Gly Thr Arg Ala Met Val Ty - #r Tyr Met Ser Thr Thr     #       125     - Ile Ile Ala Ala Val Leu Gly Val Ile Leu Va - #l Leu Ala Ile His Pro     #   140     - Gly Asn Pro Lys Leu Lys Lys Gln Leu Gly Pr - #o Gly Lys Lys Asn Asp     145                 1 - #50                 1 - #55                 1 -     #60     - Glu Val Ser Ser Leu Asp Ala Phe Leu Asp Le - #u Ile Arg Asn Leu Phe     #               175     - Pro Glu Asn Leu Val Gln Ala Cys Phe Gln Gl - #n Ile Gln Thr Val Thr     #           190     - Lys Lys Val Leu Val Ala Pro Pro Pro Asp Gl - #u Glu Ala Asn Ala Thr     #       205     - Ser Ala Glu Val Ser Leu Leu Asn Glu Thr Va - #l Thr Glu Val Pro Glu     #   220     - Glu Thr Lys Met Val Ile Lys Lys Gly Leu Gl - #u Phe Lys Asp Gly Met     225                 2 - #30                 2 - #35                 2 -     #40     - Asn Val Leu Gly Leu Ile Gly Phe Phe Ile Al - #a Phe Gly Ile Ala Met     #               255     - Gly Lys Met Gly Asp Gln Ala Lys Leu Met Va - #l Asp Phe Phe Asn Ile     #           270     - Leu Asn Glu Ile Val Met Lys Leu Val Ile Me - #t Ile Met Trp Tyr Ser     #       285     - Pro Leu Gly Ile Ala Cys Leu Ile Cys Gly Ly - #s Ile Ile Ala Ile Lys     #   300     - Asp Leu Glu Val Val Ala Arg Gln Leu Gly Me - #t Tyr Met Val Thr Val     305                 3 - #10                 3 - #15                 3 -     #20     - Ile Ile Gly Leu Ile Ile His Gly Gly Ile Ph - #e Leu Pro Leu Ile Tyr     #               335     - Phe Val Val Thr Arg Lys Asn Pro Phe Ser Le - #u Phe Ala Gly Ile Phe     #           350     - Gln Ala Trp Ile Thr Ala Leu Gly Thr Ala Se - #r Ser Ala Gly Thr Leu     #       365     - Pro Val Thr Phe Arg Cys Leu Glu Glu Asn Le - #u Gly Ile Asp Lys Arg     #   380     - Val Thr Arg Phe Val Leu Pro Val Gly Ala Th - #r Ile Asn Met Asp Gly     385                 3 - #90                 3 - #95                 4 -     #00     - Thr Ala Leu Tyr Glu Ala Val Ala Ala Ile Ph - #e Ile Ala Gln Met Asn     #               415     - Gly Val Val Leu Asp Gly Gly Gln Ile Val Th - #r Val Ser Leu Thr Ala     #           430     - Thr Leu Ala Ser Val Gly Ala Ala Ser Ile Pr - #o Ser Ala Gly Leu Val     #       445     - Thr Met Leu Leu Ile Leu Thr Ala Val Gly Le - #u Pro Thr Glu Asp Ile     #   460     - Ser Leu Leu Val Ala Val Asp Trp Leu Leu As - #p Arg Met Arg Thr Ser     465                 4 - #70                 4 - #75                 4 -     #80     - Val Asn Val Val Gly Asp Ser Phe Gly Ala Gl - #y Ile Val Tyr His Leu     #               495     - Ser Lys Ser Glu Leu Asp Thr Ile Asp Ser Gl - #n His Arg Val His Glu     #           510     - Asp Ile Glu Met Thr Lys Thr Gln Ser Ile Ty - #r Asp Asp Met Lys Asn     #       525     - His Arg Glu Ser Asn Ser Asn Gln Cys Val Ty - #r Ala Ala His Asn Ser     #   540     - Val Ile Val Asp Glu Cys Lys Val Thr Leu Al - #a Ala Asn Gly Lys Ser     545                 5 - #50                 5 - #55                 5 -     #60     - Ala Asp Cys Ser Val Glu Glu Glu Pro Trp Ly - #s Arg Glu Lys     #               570     - (2) INFORMATION FOR SEQ ID NO:7:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 1674 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: cDNA     -     (ix) FEATURE:               (A) NAME/KEY: 5'UTR               (B) LOCATION: 1..15     -     (ix) FEATURE:               (A) NAME/KEY: CDS               (B) LOCATION: 16..1590     -     (ix) FEATURE:               (A) NAME/KEY: 3'UTR               (B) LOCATION: 1591..1674     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:     #GGA TGC CCG AGT TGG      51AA CCG GCG AGG AAA     #Gly Lys Pro Ala Arg Lys Gly Cys Pro Ser T - #rp     #                10     - AAG CGC TTC CTG AAG AAT AAC TGG GTG TTG CT - #G TCC ACC GTG GCC GCG       99     Lys Arg Phe Leu Lys Asn Asn Trp Val Leu Le - #u Ser Thr Val Ala Ala     #         25     - GTG GTG CTA GGC ATT ACC ACA GGA GTC TTG GT - #T CGA GAA CAC AGC AAC      147     Val Val Leu Gly Ile Thr Thr Gly Val Leu Va - #l Arg Glu His Ser Asn     #     40     - CTC TCA ACT CTA GAG AAA TTC TAC TTT GCT TT - #T CCT GGA GAA ATT CTA      195     Leu Ser Thr Leu Glu Lys Phe Tyr Phe Ala Ph - #e Pro Gly Glu Ile Leu     # 60     - ATG CGG ATG CTG AAA CTC ATC ATT TTG CCA TT - #A ATT ATA TCC AGC ATG      243     Met Arg Met Leu Lys Leu Ile Ile Leu Pro Le - #u Ile Ile Ser Ser Met     #                 75     - ATT ACA GGT GTT GCT GCA CTG GAT TCC AAC GT - #A TCC GGA AAA ATT GGT      291     Ile Thr Gly Val Ala Ala Leu Asp Ser Asn Va - #l Ser Gly Lys Ile Gly     #             90     - CTG CGC GCT GTC GTG TAT TAT TTC TGT ACC AC - #T CTC ATT GCT GTT ATT      339     Leu Arg Ala Val Val Tyr Tyr Phe Cys Thr Th - #r Leu Ile Ala Val Ile     #        105     - CTA GGT ATT GTG CTG GTG GTG AGC ATC AAG CC - #T GGT GTC ACC CAG AAA      387     Leu Gly Ile Val Leu Val Val Ser Ile Lys Pr - #o Gly Val Thr Gln Lys     #   120     - GTG GGT GAA ATT GCG AGG ACA GGC AGC ACC CC - #T GAA GTC AGT ACG GTG      435     Val Gly Glu Ile Ala Arg Thr Gly Ser Thr Pr - #o Glu Val Ser Thr Val     125                 1 - #30                 1 - #35                 1 -     #40     - GAT GCC ATG TTA GAT CTC ATC AGG AAT ATG TT - #C CCT GAG AAT CTT GTC      483     Asp Ala Met Leu Asp Leu Ile Arg Asn Met Ph - #e Pro Glu Asn Leu Val     #               155     - CAG GCC TGT TTT CAG CAG TAC AAA ACT AAG CG - #T GAA GAA GTG AAG CCT      531     Gln Ala Cys Phe Gln Gln Tyr Lys Thr Lys Ar - #g Glu Glu Val Lys Pro     #           170     - CCC AGC GAT CCA GAG ATG AAC ATG ACA GAA GA - #G TCC TTC ACA GCT GTC      579     Pro Ser Asp Pro Glu Met Asn Met Thr Glu Gl - #u Ser Phe Thr Ala Val     #       185     - ATG ACA ACT GCA ATT TCC AAG AAC AAA ACA AA - #G GAA TAC AAA ATT GTT      627     Met Thr Thr Ala Ile Ser Lys Asn Lys Thr Ly - #s Glu Tyr Lys Ile Val     #   200     - GGC ATG TAT TCA GAT GGC ATA AAC GTC CTG GG - #C TTG ATT GTC TTT TGC      675     Gly Met Tyr Ser Asp Gly Ile Asn Val Leu Gl - #y Leu Ile Val Phe Cys     205                 2 - #10                 2 - #15                 2 -     #20     - CTT GTC TTT GGA CTT GTC ATT GGA AAA ATG GG - #A GAA AAG GGA CAA ATT      723     Leu Val Phe Gly Leu Val Ile Gly Lys Met Gl - #y Glu Lys Gly Gln Ile     #               235     - CTG GTG GAT TTC TTC AAT GCT TTG AGT GAT GC - #A ACC ATG AAA ATC GTT      771     Leu Val Asp Phe Phe Asn Ala Leu Ser Asp Al - #a Thr Met Lys Ile Val     #           250     - CAG ATC ATC ATG TGT TAT ATG CCA CTA GGT AT - #T TTG TTC CTG ATT GCT      819     Gln Ile Ile Met Cys Tyr Met Pro Leu Gly Il - #e Leu Phe Leu Ile Ala     #       265     - GGG AAG ATC ATA GAA GTT GAA GAC TGG GAA AT - #A TTC CGC AAG CTG GGC      867     Gly Lys Ile Ile Glu Val Glu Asp Trp Glu Il - #e Phe Arg Lys Leu Gly     #   280     - CTT TAC ATG GCC ACA GTC CTG ACT GGG CTT GC - #A ATC CAC TCC ATT GTA      915     Leu Tyr Met Ala Thr Val Leu Thr Gly Leu Al - #a Ile His Ser Ile Val     285                 2 - #90                 2 - #95                 3 -     #00     - ATT CTC CCG CTG ATA TAT TTC ATA GTC GTA CG - #A AAG AAC CCT TTC CGA      963     Ile Leu Pro Leu Ile Tyr Phe Ile Val Val Ar - #g Lys Asn Pro Phe Arg     #               315     - TTT GCC ATG GGA ATG GCC CAG GCT CTC CTG AC - #A GCT CTC ATG ATC TCT     1011     Phe Ala Met Gly Met Ala Gln Ala Leu Leu Th - #r Ala Leu Met Ile Ser     #           330     - TCC AGT TCA GCA ACA CTG CCT GTC ACC TTC CG - #C TGT GCT GAA GAA AAT     1059     Ser Ser Ser Ala Thr Leu Pro Val Thr Phe Ar - #g Cys Ala Glu Glu Asn     #       345     - AAC CAG GTG GAC AAG AGG ATC ACT CGA TTC GT - #G TTA CCC GTT GGT GCA     1107     Asn Gln Val Asp Lys Arg Ile Thr Arg Phe Va - #l Leu Pro Val Gly Ala     #   360     - ACA ATC AAC ATG GAT GGG ACC GCG CTC TAT GA - #A GCA GTG GCA GCG GTG     1155     Thr Ile Asn Met Asp Gly Thr Ala Leu Tyr Gl - #u Ala Val Ala Ala Val     365                 3 - #70                 3 - #75                 3 -     #80     - TTT ATT GCA CAG TTG AAT GAC CTG GAC TTG GG - #C ATT GGG CAG ATC ATC     1203     Phe Ile Ala Gln Leu Asn Asp Leu Asp Leu Gl - #y Ile Gly Gln Ile Ile     #               395     - ACC ATC AGT ATC ACG GCC ACA TCT GCC AGC AT - #C GGA GCT GCT GGC GTG     1251     Thr Ile Ser Ile Thr Ala Thr Ser Ala Ser Il - #e Gly Ala Ala Gly Val     #           410     - CCC CAG GCT GGC CTG GTG ACC ATG GTG ATT GT - #G CTG AGT GCC GTG GGC     1299     Pro Gln Ala Gly Leu Val Thr Met Val Ile Va - #l Leu Ser Ala Val Gly     #       425     - CTG CCC GCC GAG GAT GTC ACC CTG ATC ATT GC - #T GTC GAC TGG CTC CTG     1347     Leu Pro Ala Glu Asp Val Thr Leu Ile Ile Al - #a Val Asp Trp Leu Leu     #   440     - GAC CGG TTC AGG ACC ATG GTC AAC GTC CTT GG - #T GAT GCT TTT GGG ACG     1395     Asp Arg Phe Arg Thr Met Val Asn Val Leu Gl - #y Asp Ala Phe Gly Thr     445                 4 - #50                 4 - #55                 4 -     #60     - GGC ATT GTG GAA AAG CTC TCC AAG AAG GAG CT - #G GAG CAG ATG GAT GTT     1443     Gly Ile Val Glu Lys Leu Ser Lys Lys Glu Le - #u Glu Gln Met Asp Val     #               475     - TCA TCT GAA GTC AAC ATT GTG AAT CCC TTT GC - #C TTG GAA TCC ACA ATC     1491     Ser Ser Glu Val Asn Ile Val Asn Pro Phe Al - #a Leu Glu Ser Thr Ile     #           490     - CTT GAC AAC GAA GAC TCA GAC ACC AAG AAG TC - #T TAT GTC AAT GGA GGC     1539     Leu Asp Asn Glu Asp Ser Asp Thr Lys Lys Se - #r Tyr Val Asn Gly Gly     #       505     - TTT GCA GTA GAC AAG TCT GAC ACC ATC TCA TT - #C ACC CAG ACC TCA CAG     1587     Phe Ala Val Asp Lys Ser Asp Thr Ile Ser Ph - #e Thr Gln Thr Ser Gln     #   520     - TTC TAGGGCCCCT GGCTGCAGAT GACTGGAAAC AAGGAAGGAC ATTTCGTGA - #G     1640     Phe     525     #      1674        GCTT AAGGAAAAGA GAAA     - (2) INFORMATION FOR SEQ ID NO:8:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 525 amino               (B) TYPE: amino acid               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: protein     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8:     - Met Gly Lys Pro Ala Arg Lys Gly Cys Pro Se - #r Trp Lys Arg Phe Leu     #                 15     - Lys Asn Asn Trp Val Leu Leu Ser Thr Val Al - #a Ala Val Val Leu Gly     #             30     - Ile Thr Thr Gly Val Leu Val Arg Glu His Se - #r Asn Leu Ser Thr Leu     #         45     - Glu Lys Phe Tyr Phe Ala Phe Pro Gly Glu Il - #e Leu Met Arg Met Leu     #     60     - Lys Leu Ile Ile Leu Pro Leu Ile Ile Ser Se - #r Met Ile Thr Gly Val     # 80     - Ala Ala Leu Asp Ser Asn Val Ser Gly Lys Il - #e Gly Leu Arg Ala Val     #                 95     - Val Tyr Tyr Phe Cys Thr Thr Leu Ile Ala Va - #l Ile Leu Gly Ile Val     #           110     - Leu Val Val Ser Ile Lys Pro Gly Val Thr Gl - #n Lys Val Gly Glu Ile     #       125     - Ala Arg Thr Gly Ser Thr Pro Glu Val Ser Th - #r Val Asp Ala Met Leu     #   140     - Asp Leu Ile Arg Asn Met Phe Pro Glu Asn Le - #u Val Gln Ala Cys Phe     145                 1 - #50                 1 - #55                 1 -     #60     - Gln Gln Tyr Lys Thr Lys Arg Glu Glu Val Ly - #s Pro Pro Ser Asp Pro     #               175     - Glu Met Asn Met Thr Glu Glu Ser Phe Thr Al - #a Val Met Thr Thr Ala     #           190     - Ile Ser Lys Asn Lys Thr Lys Glu Tyr Lys Il - #e Val Gly Met Tyr Ser     #       205     - Asp Gly Ile Asn Val Leu Gly Leu Ile Val Ph - #e Cys Leu Val Phe Gly     #   220     - Leu Val Ile Gly Lys Met Gly Glu Lys Gly Gl - #n Ile Leu Val Asp Phe     225                 2 - #30                 2 - #35                 2 -     #40     - Phe Asn Ala Leu Ser Asp Ala Thr Met Lys Il - #e Val Gln Ile Ile Met     #               255     - Cys Tyr Met Pro Leu Gly Ile Leu Phe Leu Il - #e Ala Gly Lys Ile Ile     #           270     - Glu Val Glu Asp Trp Glu Ile Phe Arg Lys Le - #u Gly Leu Tyr Met Ala     #       285     - Thr Val Leu Thr Gly Leu Ala Ile His Ser Il - #e Val Ile Leu Pro Leu     #   300     - Ile Tyr Phe Ile Val Val Arg Lys Asn Pro Ph - #e Arg Phe Ala Met Gly     305                 3 - #10                 3 - #15                 3 -     #20     - Met Ala Gln Ala Leu Leu Thr Ala Leu Met Il - #e Ser Ser Ser Ser Ala     #               335     - Thr Leu Pro Val Thr Phe Arg Cys Ala Glu Gl - #u Asn Asn Gln Val Asp     #           350     - Lys Arg Ile Thr Arg Phe Val Leu Pro Val Gl - #y Ala Thr Ile Asn Met     #       365     - Asp Gly Thr Ala Leu Tyr Glu Ala Val Ala Al - #a Val Phe Ile Ala Gln     #   380     - Leu Asn Asp Leu Asp Leu Gly Ile Gly Gln Il - #e Ile Thr Ile Ser Ile     385                 3 - #90                 3 - #95                 4 -     #00     - Thr Ala Thr Ser Ala Ser Ile Gly Ala Ala Gl - #y Val Pro Gln Ala Gly     #               415     - Leu Val Thr Met Val Ile Val Leu Ser Ala Va - #l Gly Leu Pro Ala Glu     #           430     - Asp Val Thr Leu Ile Ile Ala Val Asp Trp Le - #u Leu Asp Arg Phe Arg     #       445     - Thr Met Val Asn Val Leu Gly Asp Ala Phe Gl - #y Thr Gly Ile Val Glu     #   460     - Lys Leu Ser Lys Lys Glu Leu Glu Gln Met As - #p Val Ser Ser Glu Val     465                 4 - #70                 4 - #75                 4 -     #80     - Asn Ile Val Asn Pro Phe Ala Leu Glu Ser Th - #r Ile Leu Asp Asn Glu     #               495     - Asp Ser Asp Thr Lys Lys Ser Tyr Val Asn Gl - #y Gly Phe Ala Val Asp     #           510     - Lys Ser Asp Thr Ile Ser Phe Thr Gln Thr Se - #r Gln Phe     #       525     - (2) INFORMATION FOR SEQ ID NO:9:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 31 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: cDNA     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9:     #          31      GTVS ARGCYTGYTT Y     - (2) INFORMATION FOR SEQ ID NO:10:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 31 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: cDNA     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:10:     #          31      DATR AARAYBGCDG C     - (2) INFORMATION FOR SEQ ID NO:11:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 63 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: cDNA     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:11:     #              50TGGCAG CCAGGGCYTC ATACAGGGCT GTGCCRTCCA     #      63     - (2) INFORMATION FOR SEQ ID NO:12:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 34 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: cDNA     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:12:     #        34        GCCA TGCAACAGCC TGTT     - (2) INFORMATION FOR SEQ ID NO:13:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 28 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: cDNA     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:13:     #             28   CACG GTCAGTTG     __________________________________________________________________________ 

What we claim is:
 1. An isolated nucleic acid molecule encoding a mammalian excitatory amino acid transporter that is the EAAT4 glutamate transporter.
 2. An isolated nucleic acid molecule according to claim 1 encoding an amino acid sequence identified as SEQ ID No.
 2. 3. A nucleic acid hybridization probe for detecting mammalian excitatory amino acid transporter expression comprising the nucleotide sequence of claim
 2. 4. A recombinant expression construct comprising a nucleic acid molecule having a nucleotide sequence encoding a mammalian excitatory amino acid transporter having an amino acid sequence identified as SEQ. ID No.
 2. 5. A cell culture transformed with the recombinant expression construct of claim
 4. 6. An amphibian oocyte expressing the mammalian excitatory amino acid transporter of claim
 1. 7. The amphibian oocyte of claim 6 that is a Xenopus laevis oocyte.
 8. An isolated nucleic acid molecule according to claim 2 having a nucleotide sequence identified as SEQ. ID No.
 1. 